Linköping University Medical Dissertations No. 847
Muscle function in Juvenile Idiopathic Arthritis
A two-year follow-up
Hans Lindehammar
Department of Neuroscience and Locomotion, Division of Neurophysiology Faculty of Health Sciences Linköpings Universitet, SE-581 85 Linköping, Sweden
Linköping 2004 © Hans Lindehammar 2004
Published articles have been reprinted with permission of the copyright holder: Journal of Rheumatology and Acta Paediatrica
Printed in Sweden by Unitryck, Linköping, Sweden, 2004
ISSN 0345-0082 ISBN 91-7373-819-0
2 Imagine no possessions I wonder if you can No need for greed or hunger A brotherhood of man Imagine all the people Sharing all the world…
John Lennon
3 4 Abstract
This is a study of muscle function in Juvenile Idiopathic Arthritis (JIA). Rheumatoid arthritis (RA) is a disease that primarily affects the synovial membrane of joints. Muscle weakness, atrophy and pain occur in adult RA. This may be a consequence of joint pain, stiffness and immobility. Muscle inflammation and neuropathy occur as complications in adults. Muscle function in JIA has been much less studied.
The aim of the study was to examine whether muscle weakness and atrophy also occur in children with JIA.
This was a longitudinal study over a two-year period, where muscle strength and thickness were measured repeatedly in a group of 20 children and teenagers with JIA. Muscle strength was measured using different methods and in several muscle groups. Muscle biopsies were obtained and nerve conduction velocity studies performed.
The study concludes that, compared to healthy people, children and teenagers with JIA have as a group reduced muscle strength and muscle thickness. For most of these children and teenagers, muscle strength is only slightly lower than expected, but a few have marked muscle weakness. This is most apparent in patients with severe polyarthritis where the weakness seems to be widespread. Patients with isolated arthritis may also have greatly reduced strength and thickness of muscles near the inflamed joint. There is a risk of decreasing strength in patients with polyarthritis and in muscles near an active arthritis. Minor changes are common in muscle biopsies, and findings may indicate immunological activity in the muscles. Atrophy of type II fibres, as in adult RA, was not found in JIA. No patient had signs of neuropathy.
5 6 Original publications
This thesis is based on the following papers:
I. Lindehammar H, Bäckman E. Muscle function in Juvenile Chronic Arthritis. Journal of Rheumatology 1995;22:1159–65
II. Lindehammar H, Sandstedt P. Measurement of Quadriceps Muscle Strength and Bulk in Juvenile Chronic Arthritis. A Prospective, Longitudinal, 2 Year Survey. Journal of Rheumatology 1998;25:2240–8
III. Lindehammar H. Hand strength in juvenile chronic arthritis: a two-year follow-up. Acta Paediatrica 2003;92:1291–6
IV. Lindehammar H, Lindvall B. Muscle involvement in juvenile idiopathic arthritis. Submitted to Rheumatology 2004
7 8 Contents
ABSTRACT...... 5
ORIGINAL PUBLICATIONS...... 7
CONTENTS...... 9
INTRODUCTION...... 11 Rheumatoid arthritis...... 11 Rheumatoid arthritis in childhood...... 11 Muscles...... 12 Muscles during growth ...... 14 Strength measurement ...... 14 Strength measurement in children...... 16 Muscle function in joint disorders ...... 16 Muscle function in rheumatoid arthritis ...... 17 Muscle function in juvenile idiopathic arthritis...... 17 Immunology and muscle ...... 18 AIMS OF THE STUDY...... 19
MATERIAL...... 21
PATIENTS ...... 21 CONTROL AND REFERENCE GROUPS ...... 24 Reference groups...... 24 Controls...... 24 METHODS ...... 27
MUSCLE STRENGTH...... 27 Isometric muscle strength...... 27 Isokinetic muscle strength ...... 27 Handgrip strength ...... 27 Non-voluntary strength...... 28 MUSCLE THICKNESS...... 29 MUSCLE BIOPSY ...... 30 Muscle biopsy ...... 30 Staining...... 30 Immunohistochemistry...... 30 Fibre types and areas ...... 31 NERVE CONDUCTION STUDY ...... 31 JOINT EVALUATION ...... 31 DATA ANALYSIS...... 32 STATISTICAL ANALYSIS...... 32 STUDY DESIGN ...... 32 ETHICAL CONSIDERATION ...... 32 RESULTS AND DISCUSSION...... 33
PAPER I ...... 33 PAPER II...... 51 PAPER III...... 70 PAPER IV ...... 74 SUMMARY OF RESULTS...... 81
GENERAL CONSIDERATIONS...... 83
MAIN CONCLUSIONS ...... 87
9 ACKNOWLEDGEMENTS...... 89
REFERENCES...... 91
PAPER I
PAPER II
PAPER III
PAPER IV
10 Introduction
Impaired muscle function is a consequence of rheumatoid arthritis (RA) and other joint disorders, with muscle weakness, atrophy and pain common symptoms. Reduced joint mobility and inactivity are likely causes. RA is primarily a disease that affects the joints with inflammation of the synovial membrane. The synovitis can damage the joint capsule, the cartilage and bone. Joint stiffness and pain can impair muscle strength and reduce physical capacity. In clinical practice atrophy of the quadriceps muscle is a well-known consequence of knee arthritis. Occasionally, muscle weakness and atrophy develop near an inflamed joint even without much pain or joint stiffness. Neuromuscular complications such as neuropathy and myopathy sometimes occur in RA. It is difficult to know to what extent muscle weakness contributes to the reduced functional capacity in chronic joint disease. Rheumatoid arthritis in childhood, Juvenile Idiopathic Arthritis (JIA) is not as common as in adults and the aspects of muscle function have been much less studied. The present thesis is an attempt to increase our knowledge of muscle impairment in JIA. It is a longitudinal study with a two-year observational survey of muscle strength and thickness. The work was carried out between 1988 and 1992. The analyses were carried out later.
Rheumatoid arthritis Rheumatoid arthritis in adults is a chronic idiopathic arthritis occurring in about 0.8% of the population. In most cases it is a symmetric distal polyarthritis, but all joints can be affected. The aetiology is not clearly understood, but there is a genetic component and some unknown factors that triggers activation of the immune system. Many patients have autoantibodies as rheumatoid factor (RF) in the blood. Inflammation starts in the synovial membrane lining the joint. The synovitis damages cartilage, bone and tendons. There is also sometimes inflammation in other tissues in the body. In most cases the disease is chronic, but the outcome can be influenced by treatment. The arthritis causes reduced mobility of the joints and deformities. Pain, stiffness, weakness and reduced functional capacity are common.
Rheumatoid arthritis in childhood Chronic arthritis of unknown aetiology also occurs in children but is much rarer than RA in adults, with a prevalence of about 0.06% of children [1]. This is a heterogeneous group of chronic arthropathies.
11 The disease has several names depending on the criteria for diagnosis. The most commonly used term at present is juvenile idiopathic arthritis (JIA). This is defined as a disease predominately of arthritis with an onset before 16 years of age, a duration of at least six weeks, and having no known cause. The term was proposed by the International League of Associations for Rheumatology (ILAR) [2]. The term juvenile chronic arthritis (JCA) was proposed by the European League Against Rheumatism (EULAR); it has almost the same definition but requires a duration of three months. The subtypes have somewhat different labels, but both terms include arthritis associated with psoriasis, spondylitis and inflammatory bowel disease. The term juvenile rheumatoid arthritis (JRA), proposed by the American Rheumatism Association (ARA), was the earliest classification and is mostly used in North America. Although the cause of the disease is unknown, there are genetic factors and some unknown environmental factors that trigger the activation of the immune system. Probably, there are different factors for the different subtypes of the disease. The subtypes according to the JIA criteria are polyarthritis (RF positive or RF negative), oligoarthritis, systemic onset, psoriatic arthritis, enthesitis-related arthritis, and other arthritis. Polyarthritis is the subtype that most resembles adult RA with symmetric distal arthritis. Five or more joints must be inflamed. Some of these children are RF positive, and their disease is often more severe. Oligoarthritis has one to four asymmetrically located inflamed joints. This is the most common subtype and mainly involves large joints, most commonly the knee. One subgroup is young girls, with positive antinuclear antibodies (ANA) and a considerable risk of uveitis. The systemic onset type is called Still’s disease, with fever for at least two weeks and signs of systemic involvement. It often subsequently proceeds to severe chronic polyarthritis. The prognosis is generally better than adult RA, but remains uncertain and depends on the subtype and age of onset. About half of patients are expected to have continuing disease after five years [3]. In a long-term study by Koivuniemi et al [4], 60% of patients with JCA followed into adult life were in remission at follow-up. The prognosis is better for some children with an oligoarthritis subtype, and worse for polyarthritis. There is sometimes a progression from one subtype to another. About 50% of children with oligoarticular onset will progress to polyarthritis [5].
Muscles The function of the skeletal muscle is to generate force. The long contractile cells building the muscles are the muscle fibres. They are tubular and vary from a few to several centimetres in
12 length and from 50 to 70 µm in diameter. The muscle fibres contain the contractile apparatus, the myofibrils. Each muscle fibre contains bundles of myofibrils that are surrounded by membranes in contact with the cell membrane of the muscle fibre. The contractile property is dependent on the protein actin and myosin arranged in myofilaments. These proteins have the ability to shorten in the presence of calcium ions. Calcium ions are released inside the cell as a response to stimulation of the motor nerve, and the increase in intracellular calcium concentration activates the contractile proteins. The process of contraction is energy requiring. The mitochondria are energy producers in muscle fibres, and the energy is released from degradation of adenosine triphosphate (ATP) by action of the enzyme ATPase. Muscle fibres are grouped into functional units, the motor units, consisting of one motor neurone with the cell body in the anterior horn of the spinal cord, its axon, and a group of muscle fibres innervated by this nerve cell. The number of muscle fibres in one motor unit is between five and several thousand, scattered within an area of 5 to10 mm. The motor unit is the smallest functional unit of the muscle, since all muscle fibres in one motor unit contract at the same time. Increasing the frequency of discharges in the motor neurone, and activating more and more motor units, gradually increases the muscle force. Muscle contraction can be isometric, i.e. static without shortening of the muscle or movement, or dynamic with a shortening of the muscle and movement of the limb. The muscle fibres are of three basic types, classified according to their characteristics. Type I fibres are red, slow twitch, resistant to fatigue and metabolically aerobic-oxidative. Type IIA fibres are white, fast twitch, fatigue resistant, and both oxidative and glycolytic. Type IIB fibres are white, fast twitch, fatigue sensitive and glycolytic. These three fibre types occur in approximately equal proportions in muscles, though this may vary in different muscles. All muscle fibres in a motor unit are of the same fibre type. Sometimes immature muscle fibres, called type IIC fibres, are seen in biopsies.
13 Figure 1. Muscle fibres in cross section. Type I fibres are light and type II fibres are dark.
Muscles during growth Muscle volume increases between birth and puberty. This occurs by an increase in muscle fibre diameter and length – the number of muscle fibres does not increase [6]. The amount of myofilaments increases and with this muscle strength. Only small changes occur after puberty [7, 8], but adult males usually have larger muscle fibres than females. In healthy adults, type II fibres have slightly larger areas than type I fibres, especially in men [9]. From childhood to adulthood, the proportion of type I fibres decreases and the proportion of type II fibres increases, probably caused by a transformation of type I to type II fibres [6].
Strength measurement Muscle function includes different muscles properties, for example strength and endurance. Muscle strength can be estimated by manual testing, providing an approximate grading of weakness. Functional tests, for instance walking speed, can also be used to evaluate muscle function in different muscle groups.
14 If more detailed information on the strength of different muscles is required, more quantitative methods must be used. For muscle strength measurements, isometric, isotonic and isokinetic tests are available. Strength can be measured during shortening (concentric contraction) or during lengthening (eccentric contraction) of the muscle. Isometric measurement implies no movement and only slight shortening of the tested muscle. The test can be performed with a simple dynamometer that prevents the tested limb from moving, i.e. a static contraction. This is an easy and accurate way of measuring strength, but gives no information on the dynamic capacity of the muscle. It measures the tension developed at one point only of the dynamic range. The test can be performed in two different ways. In this study the breaking force technique was used. This implies that the tested person takes the specified position and is asked to maintain this position when force is applied. The maximal strength is measured when the force on the transducer is so great that the position cannot be held. The other type of measurement is contraction, where the tested person is asked to contract against the transducer as hard as possible. Isotonic measurement means that the muscle contracts against a constant load, but at variable speed. This is much like movements in daily life, for example lifting an object. Since the speed is not predetermined it is difficult to standardise the test situation. Isokinetic measurement requires more sophisticated dynamometers. The strength is measured with a movement at a controlled and fixed speed. It measures strength through the whole range of motion and gives information on the dynamic capacity of the muscle, though the test situation is somewhat artificial. Strength is measured in newtons (N) as a measure of the developed force in the movement. However, the measured value is not only dependent on the power produced by the muscle, but also on the length of the limb and where on the limb the test device is placed. For this reason torque is sometimes measured instead, taking into consideration the length of the lever. Torque is measured in newton metres (Nm). In some cases it may be necessary to correct the measured strength because of the effect of gravitation, especially when proximal limb muscles are tested in weak individuals. All these tests are carried out to measure maximal voluntary strength. The results are therefore highly dependent on the individual’s motivation to perform a maximal contraction of the muscle. It is also important that the test positions and placements of the test device are standardised. There is a learning effect in strength measurement, as it is common to perform better in subsequent tests than on the first occasion. Measuring strength during electrical stimulation of the nerve can also be used to test muscle function. This is a way of reducing the
15 effect of motivation during the test. However, the procedure is a little painful and is best performed on small muscles.
Strength measurement in children The methods described above can also be used on children. In very young children the results may be unreliable because of an inability to cooperate during the test. Muscle strength increases during a child’s growth, and reference values must therefore be age-related. It is not only the power of the muscle itself that increases during growth, but also the length of the limbs, making the lever longer. When measuring strength over a period of time one must take the expected change in strength, caused by growth, into consideration. The topic has been reviewed by Jones et al [10]. Not all methods of strength measurement have been tested for reliability in children. However, the isometric strength test with a handheld dynamometer used in this study has. The coefficient of variation ranged between 6 and 16% [11]. The reliability can be increased by using one single examiner and by standardising the test procedure.
Muscle function in joint disorders In clinical practice weakness and atrophy of the quadriceps muscle of the thigh is frequently observed in knee joint disorders. This has been studied in osteoarthritis of the knee [12-14], where reduced knee extensor muscle strength and volume have been found compared to healthy people. The same was found in patients with knee ligament injuries [15, 16]. Nakamura et al [17] found muscle fibre atrophy of the quadriceps muscle in knee joint disorders. This is probably caused partially by knee joint pain and inactivity. However, Slemenda et al [13] found weakness in knee extensors in persons with osteoarthritis without pain. The effect of unloading on skeletal muscles has been studied in healthy persons. In one study on healthy subjects, strength, cross-sectional area and muscle biopsies were analysed in the quadriceps muscle after six weeks of bed rest [18]. Knee extensor torque was reduced by 25%, cross-sectional muscle area was reduced by 14% and muscle fibre cross-sectional area was reduced by 18%. The effect of artificially induced knee effusion on muscle strength has also been studied experimentally in healthy subjects. Both reduction of knee extensor strength and inhibition of reflex-evoked muscle contraction were found [19, 20]. A relationship between the degree of knee effusion and reduction in knee extensor muscle strength has also been found in chronic knee arthritis. Geborek et al [21] found that a progressive inhibition
16 occurred in knee extensor torque when the intra-articular volume and pressure increased. Fahrer et al [22] found that joint aspiration of knee effusion immediately increased quadriceps muscle strength. This arthrogenous muscle weakness is apparently caused by reflex inhibition, since it is partly dependent on afferent stimuli from the joint [23]. Experimental studies in rats [24] have shown rapid muscle atrophy one week after artificially induced arthritis. Muscle strength and volume in joint disorders in children has not been extensively studied. Robben et al [25] showed that muscle atrophy was present in the quadriceps muscle in children with painful hip.
Muscle function in rheumatoid arthritis Reduced strength and muscle volume are known to occur in adult RA. This is most obvious in muscles near an inflamed joint and is mainly described in thigh muscle in knee arthritis though also in other muscles [26-29]. The mechanisms are probably the same as for other joint disorders. The muscles of the forearm were studied by Helliwell et al [30], who found reduced grip strength and a reduction in forearm muscle bulk, though muscle wasting was small compared to the reduction in strength. Inactivity due to the disease can lead to a generalised reduction in muscle volume and strength. This is often obvious in patients with severe polyarthritis. Inflammation of the muscles, i.e. polymyositis and dermatomyositis, is known to occur as a complication in adult RA [31-34]. In muscle biopsies there are signs of inflammation and muscle fibre degeneration. Changes in muscles are also known to occur as a complication with medicines used in RA, e.g. corticosteroids, chloroquine and d-penicillamine. Complications from the nervous system are known to occur in RA and may have affect muscle function. Studies have shown the presence of vasculitic neuropathy, distal symmetric neuropathy and compression neuropathy in some cases of adult RA [35-38]. Some authors have tried to relate the muscle weakness to functional capacity [39-42]. Ekdahl et al [26] found a significant correlation between muscle strength and activities of daily living.
Muscle function in juvenile idiopathic arthritis Muscle function in juvenile idiopathic arthritis has been studied much less than in adults, but localised muscle atrophy of thigh muscle in knee arthritis is well known in clinical practice. Overgrowth of the leg resulting in leg-length discrepancy is known to occur as a result of knee arthritis in childhood [43]. In a few studies on muscle strength in children with juvenile
17 idiopathic arthritis, reduced muscle strength, physical capacity and gait velocity have been found [44-51].
Immunology and muscle Major histocompatibility complexes (MHC) are important molecules in the immunological response to antigens. These glycoproteins bind antigens and present them for immune reactive cells. There are two main types: MHC class I and class II. These molecules are not found on muscle cells in normal muscles. They have been found on muscle fibres in inflammatory myopathies in adults [52, 53] and also in muscles from adult patients with RA [54]. Membrane attack complex (MAC) is formed during complement activation, which is part of the immunological response to antigens. It is not found in normal muscles, but has been found in myositis associated with Sjogren’s syndrome and in juvenile dermatomyositis [55, 56].
18 Aims of the study
The aims of the present study were:
- to determine whether there is muscle weakness and atrophy in children with JIA (paper I)
- to analyse how the intensity of arthritis in JIA influences juxta-articular muscle strength and muscle thickness (paper II)
- to describe muscle strength in the hands of children with JIA, changes over time, and the relationship to local arthritis and disease subtype (paper III)
- to study changes in muscle structure and nerve function in JIA (paper IV)
19 20 Material
Patients All patients in the study were selected from the Swedish county of Östergötland, which has 400 000 inhabitants. Paediatricians and paediatric clinics in the county were asked to report all patients with JIA/JCA. This yielded 26 children and teenagers between 7 and 18 years of age. Children below the age of seven were not expected to be able to perform all the tests correctly and were therefore not included in the study. All of the 26 children and teenagers fulfilled the EULAR (European League Against Rheumatism) criteria for active JCA, with onset before 16 years of age, duration of arthritis of more than three months, and exclusion of other diseases. Twenty of the 26 (77%) gave informed consent and joined the study. Six did not wish to participate. The patients were between 7 and 16 years of age at the start of the study. Ten were girls and ten were boys. The patient characteristics are shown in Tables 1 and 2. Two of the patients had severe disabling disease.
21 Table 1. Patients in the study
Patient Sex Age Age at Height (cm) Weight (kg) Patient’s number in onset paper I–III IV JH F 7.2–9.3 5 121–131 20–28 1 1
MB F 8.2–10.2 2 115–126 18–22 2
PM F 8.5–11.2 7 140–160 27–41 3 2
SP F 12.7–14.8 7 132–142 36–35 4 3
MGT F 13.6–15.6 12 159–166 39–50 5
CF F 14.7–16.8 14 162–163 44–49 6 4
HG F 14.9–16.9 13 172–174 54–60 7 6
SH F 15.6–17.6 12 165–166 72–72 8 7
LE F 15.8–17.8 14 166–166 46–48 9 8
MW F 15.7–17.7 14 166–166 62–65 10 5
ML M 9.8–12.0 9 138–145 29–32 11
JL M 10.8–13.1 4 146–163 34–42 12 9
JK M 11.7–13.7 5 154–165 55–64 13
JW M 13.8–15.9 13 163–175 54–63 14 12
FJ M 14.0–16.0 9 151–163 50–65 15 10
MGN M 14.3–16.3 6 161–166 46–52 16 11
BP M 14.8–16.8 14 159–173 53–70 17 13
AA M 14.8–16.8 9 180–185 54–65 18 14
JO M 16.3–18.3 10 168–170 45–52 19 15
HP M 16.3–18.3 14 169–171 75–83 20
F: female, M: male
22 Table 2. Patients in the study
Patient Subgroup/ Disease history Treatment serotype JH Oligo/ Arthritis in right elbow and both knees, stable NSAID, IAS neg disease, good capacity MB Poly/ Systemic onset, symmetric polyarthritis, small and CS, D-pen, ASA, neg large joints, stable disease, slightly reduced IAS capacity PM Oligo/ Arthritis in right hip, both knees, stable disease, NSAID neg good capacity SP Poly/ Symmetric polyarthritis, small and large joints, CS, NSAID, PD, HLA B27 active disease, reduced capacity D-pen, IAS MGT Oligo/ Arthritis in both knees, stable disease, good HCQ, IAS neg capacity CF Poly/ Symmetric polyarthritis, fingers, knees, TMJ, NSAID neg stable disease, slightly reduced capacity HG Poly/ Symmetric polyarthritis, fingers, hips, knees, stable NSAID neg disease, slightly reduced capacity SH Poly/ Asymmetric polyarthritis, small and large joints, NSAID, AU neg active disease, reduced capacity LE Oligo/ Arthritis in knees, toes, wrist, stable disease, good NSAID neg capacity MW Oligo/ Arthritis in wrists, right knee, stable disease, good NSAID, HCQ neg capacity ML Oligo/ Arthritis in right knee and left hip, active disease, ASA, HCQ, SSZ, neg reduced capacity IAS JL Mono/neg Arthritis in left knee, stable disease, good capacity ASA JK Oligo/ Systemic onset, arthritis in ankles, hips, stable NSAID neg disease, good capacity JW Oligo/ Arthritis in finger, toes, right knee, stable disease, NSAID, AU HLA B27 good capacity FJ Oligo/ Arthritis in ankles, hips, stable disease, good ASA HLA B27 capacity MGN Oligo/ Arthritis in knees, wrist, ankle, finger, stable ASA, HCQ, SSZ, neg disease, reduced capacity IAS BP Oligo/ Arthritis in ankles, elbow, stable disease, good NSAID, SSZ, HLA B27 capacity IAS AA Poly/ Arthritis in wrist, ankles, knees, stable disease, NSAID, SSZ, neg reduced capacity IAS JO Poly/ Symmetric polyarthritis, small and large joints, CS, NSAID, RF, ANA stable disease, reduced capacity SSZ, D-pen, IAS HP Oligo/neg Arthritis in ankles, stable disease, reduced capacity NSAID, SSZ
Oligo: oligoarticular, Poly: polyarticular, Mono: monoarticular, TMJ: temporomandibular joint, IAS: intra-articular steroids, CS: corticosteroid, NSAID: non-steroidal anti-inflammatory drugs, ASA: acetylsalicylic acid, AU: auranofin, D-pen: D-penicillamine, SSZ: sulphasalazine, HCQ: hydroxychloroquine, PD: podophylline
23 Control and reference groups
Reference groups The methods used in the current study were chosen to match existing published reference values for healthy children and young adults. The ages and number of persons included in the different reference groups are summarised in Table 3. For the isometric, isokinetic, non-voluntary and handgrip strength measurements, the late Eva Bäckman examined healthy children and young adults with the same equipment used in the present study. The reference values were published earlier [11, 57-60]. For measurement of muscle thickness with ultrasound, the reference values published by Heckmatt et al were used [61]. The control group was also used to establish the reference values for muscle thickness in children over the age of 12. For muscle biopsies we used a group of healthy physiotherapy students. This group was first examined to serve as controls in a different hitherto unpublished study, and biopsies were therefore taken from the gastrocnemius muscle rather than the anterior tibial muscle as in the patients. The biopsies were prepared at the same laboratory, using the same methods as the patients. It was not considered ethical to perform muscle biopsies on healthy age-matched children.
Table 3. Age and number of healthy children and adults in the different reference group
Isometric Isokinetic Handgrip Non- Muscle Muscle strength strength strength voluntary thickness biopsy strength Original 3.5–70 years 6–34 years 9–18 years 9–15 years 0–12 years 18–39 years reference (n = 345) (n = 163) (n = 97) (n = 77) (n = 276) (n = 58)
Used in the 7–18 years 7–18 years 9–18 years 9–15 years 7–12 years 18–23 years present study (n = 174) (n = 94) (n = 97) (n = 77) (n = 118) (n = 33)
Controls Twenty healthy children volunteered in the study as controls. They were most often a classmate of the patient, and not randomly selected. The controls were matched for age and sex. The age difference was less than one year. Isometric muscle strength in knee extensors, ankle dorsiflexors, elbow flexors and wrist dorsiflexors were measured. Thickness of the
24 quadriceps muscle was measured with ultrasound. They were examined using the same equipment and methods, and generally at the same time as the patients. They were examined every three months for two years, as were the patients. The examiner was the same as for the patients (HL). The reasons why they were examined were that the reference group for ultrasound measurement was up to 12 years of age and, secondly, to evaluate the effect of growth on strength and muscle thickness.
25 26 Methods
Muscle strength Muscle strength was measured in several muscle groups and by different methods. All test procedures, positions and equipment were chosen to match the existing reference values. In the voluntary strength measurements the tested person was encouraged to perform a maximal contraction.
Isometric muscle strength Isometric muscle strength was measured using a hand-held electronic dynamometer (Myometer®, Penny & Giles Ltd, Christchurch, Dorset, UK). The maximal voluntary strength was measured by the breaking force technique. The padded transducer head was placed on defined sites and resistance was applied until it was lost. The test positions were standardised (see Table 4). Three measurements were taken at each location, at intervals of 3–5 minutes, and the peak value recorded. Both the right and left sides were tested. The test was repeated every three months for two years in patients and controls. The muscle groups tested were knee extensors, ankle dorsiflexors, elbow flexors and wrist dorsiflexors. The variation between repeated tests is about 10% for this method [62]. The test was carried out by HL.
Isokinetic muscle strength Isokinetic muscle strength in ankle dorsiflexors was measured using a Cybex® II dynamometer (Lumex Inc., Bayshore, New York). The position was the same as for isometric strength measurement in ankle dorsiflexors. Maximal strength was measured at six different speeds: constant angular velocities at 15, 30, 60, 120, 180 and 240 degrees/sec. Two measurements were made on each side. The maximal developed torque was measured and the peak value used for presentation. The test was conducted three times one year apart in the patients. The test was carried out by Eva Bäckman.
Handgrip strength Handgrip strength was measured with a mechanical dynamometer (Rank Stanley, Cox, UK). The child was instructed to grip the device as hard as possible. The dominant hand was tested, e.g. the right hand in right-handed individuals. The test was performed in patients three times one year apart. The test was conducted by Eva Bäckman.
27 Non-voluntary strength Strength was measured using a special device measuring the force in thumb adduction during electrical stimulation of the ulnar nerve. The hand and arm were fixated and with the thumb in abduction. A supramaximal electrical stimulation at 50 Hz was given to the ulnar nerve, causing a contraction of the thumb adductor muscle. The developed force was measured with a mechanical dynamometer. The construction of the device made it possible to test the right hand only. The test was performed twice two years apart in the patients. The youngest patient refused to do this test. The test was carried out by Eva Bäckman.
28 Table 4. Test positions for muscle strength measurements
Knee extensors (isometric) Position: sitting Knee extended. Resistance applied on anterior aspect of lower leg, just above the malleoli. Fixation: posterior aspect of thigh, just above the knee.
Ankle dorsiflexors (isometric) Ankle dorsiflexors (isokinetic) Position: sitting Position: sitting Knee flexed 90 deg., foot in neutral Knee flexed 90 deg. position. Resistance applied on Resistance applied on dorsal aspect of dorsal aspect of foot, foot, proximal to metatarsophalangeal proximal to joints. metatarsophalangeal joints. Fixation: posterior aspect of lower leg Fixation: thigh and lower just above the ankle. leg. Elbow flexors (isometric) Position: sitting Elbow flexed 90 deg., arm supinated. Resistance applied on volar aspect of forearm, just above the wrist. Fixation: posterior aspect of upper arm, just above the elbow
Wrist dorsiflexors (isometric) Position: supine Elbow extended, wrist in 90 deg. dorsiflexion. Resistance applied on dorsum of hand. Fixation: ventral aspect of lower arm. Handgrip strength Non-voluntary strength (electrical stimulation) Position: sitting Position: sitting Elbow flexed 90 deg., arm supinated. Elbow slightly flexed, arm supinated. Gripping the device as hard as possible. Thumb abducted, arm and hand fixated in a special device. Electrical stimulation of the ulnar nerve causing the thumb to adduct.
Muscle thickness The muscle bulk of the quadriceps muscle was measured by ultrasound imaging (ATL Ultrasound, Advanced Technology Laboratories, Bothell, WA, USA). The thickness of the
29 anterior part of the quadriceps muscle at mid-thigh level was measured in a standardised way. The child was supine, relaxed and the knee extended. Mid-thigh level was located by ultrasound, halfway between the top of the greater trochanter and the knee joint. The distance between the outer fascia of the quadriceps muscle and the femur was measured with electronic callipers. Special precautions were taken to avoid compressing the tissue with the transducer and to keep it perpendicular to the skin. Three measurements were taken on each side and the mean value calculated. This test was conducted every three months for two years in patients and controls. The examination was performed by HL at the same time as the isometric strength measurements.
Muscle biopsy
Muscle biopsy Biopsies were obtained once from the anterior tibial muscle using local anaesthesia and the semi-open conchotome biopsy technique [63]. A standard histopathological examination was carried out for all biopsies. Serial sections (more than 100 sections) were analysed by light microscopy. In the control group, biopsies from the gastrocnemius muscle were examined in a similar way.
Staining Routine stainings were performed after formalin fixation and paraffin embedding. Stainings were carried out with Mayer’s haematoxylin-eosin, Weigert’s haematoxylin-van Gieson and Weigert’s elastin-van Gieson. Frozen specimens were stained for myofibrillar adenosine triphosphatase (after preincubation at pH 9.4 and 4.6), NADH-tetrazolium reductase, phosphorylase and acid phosphatase. A modified Gomori trichrome, Ehrlich’s haematoxylin- eosin and Weigert’s haematoxylin-van Gieson were also used on the frozen material. Periodic acid Schiff (PAS) was used for staining glycogen and oil red O for lipids.
Immunohistochemistry Immunohistochemical stainings were made on 6 m thick frozen sections for analysis of cell surface markers with monoclonal antibodies. Mouse monoclonal antibodies from DAKO Corporation (Glostrup, Denmark) were used: MHC class I (HLA-ABC M736, IgG2a, 1:100),
30 MHC class II (HLA-DR M704, IgG2a, 1:50) and MAC (anti-human C5b-9 M777, aE11, 1:25). The following criteria were used for evaluation of abnormal expression of inflammatory markers. MHC class I: expression involving the total circumference of the muscle fibre membrane in parts of the biopsy; MHC class II: dense accumulations of capillary expression in isolated parts of the biopsy; MAC: expression in capillaries. Grading of expression was made according to scales earlier described [55, 64].
Fibre types and areas The fibre types and fibre areas were measured using the Tema® system (Check Vision ApS, Hadsund, Denmark). ATPase staining at pH 4.3, 4.6 and 9.4 was used to differentiate fibre types, and an antibody against the sarcolemmal protein merosin was used to delineate fibre areas. The number, percentage and mean areas of fibre types I, IIA, IIB and IIC were measured. In each biopsy between 90 and 265 muscle fibres were analysed. Because of a sparse amount of muscle tissue in the biopsy, the muscle fibre analysis could not be reliably performed for two patients.
All evaluations of the muscle biopsies were made by one person (Björn Lindvall) using the same criteria for patients and controls.
Nerve conduction study Nerve conduction velocity was measured twice in all patients, at the start of the study and two years later. The median and ulnar nerves in the dominant arm were examined for motor and sensory conduction velocity, distal latencies and amplitudes. A nerve conduction study was also carried out in the non-dominant leg. The peroneal nerve was tested for motor nerve conduction velocity, motor response amplitude and distal latency. The sural nerve was tested for sensory nerve conduction velocity and sensory nerve action potential.
Joint evaluation The severity of the arthritis in various joints was graded according to the severity score proposed by the Pediatric Rheumatology Collaborative Study Group. This instrument has been used in other studies [45, 65, 66]. Four clinical indices were assessed: swelling (0–3), pain on movement (0–3), tenderness to palpation (0–3), and limitation of passive movement
31 (0–4). Swelling was graded as 0 = no swelling, 1 = mild swelling, 2 = moderate swelling, 3 = marked swelling. Pain on movement and tenderness to palpation were graded as 0 = none, 1 = mild (subjective complaint only), 2 = moderate (wincing or withdrawal), 3 = severe (marked response). Limitation of movement was graded as 0 = full range, 1 = 25% limitation, 2 = 50% limitation, 3 = 75% limitation, 4 = no movement. This score gives values from 0–13 for each joint. A score of 0 means no signs of arthritis. A patient with a score > 0 was considered to have arthritis in that joint. None had limitation of movement only. The joint scoring was carried out by the author (HL) every three months, at the same time as the other tests.
Data analysis Strength values and muscle thickness were compared to the reference values and expressed as a percentage of the mean of the reference group for the actual muscle, age and sex, i.e. the expected value. Values were also expressed in standard deviations from the mean of the reference group.
Statistical analysis To compare patients and controls, and patients with reference values, parametric (t-test) and non-parametric (Wilcoxon and sign tests) were used, depending on the nature of the data. To evaluate changes over time a linear regression model was used. Qualitative data were analysed in 2 x 2 contingency tables using Fisher’s exact test. A p-value less than 0.05 was considered significant.
Study design This was an observational study and no treatment effects were evaluated. The children continued their normal treatment during the whole study period. The examinations were carried out at defined intervals irrespective of symptoms or treatment. Changes in treatment were made and intra-articular steroid injections were given when necessary. Articles I and IV were cross-sectional studies. Articles II and III were longitudinal surveys carried out over a period of two years.
Ethical consideration The studies were approved by the ethics committee of the University Hospital, Linköping (registration numbers 87110 and 97140).
32 Results and discussion
Paper I The patients in the thesis were tested at 6–9 occasions, but the data presented in this paper all come from the test in the middle of the study, i.e. the fourth or fifth test. Paper I is a cross-sectional study of muscle function in JIA/JCA. Muscle strength and thickness were measured by all methods on one occasion. The results were compared to controls and reference values. To enable comparison of results of patients of different ages and gender, all measured values were related to the mean of the reference group. This is called the expected value. Muscle strength at 100% of the expected value means that the strength is identical to the mean of the reference group for the patient’s age and gender. A test result of less than 100% means that the strength or muscle thickness is lower than expected. The age difference between patient and control in each pairing was less than four months. As a group there were no significant differences between patients and controls in weight or height. For the main results see Figure 2–10 and Table 5–13.
33 Figure 2. Isometric muscle strength in knee extensors
Knee extensors
200
patient right patient left 100 control right control left
strength % of expected % of strength 0 1 2 3 4 5 6 7 8 9 1011121314151617181920 patient and control number
Knee extensors
200
right 100 left strength % of expected 0 with local arthritis without local arthritis
34 Table 5. Isometric muscle strength in knee extensors
Isometric Compared to reference values Compared to matched strength controls Knee Percentage Number Significance Percentage Significance extensors of expected below of control value expected group’s value value All patients Right 78 15/20 0.021 78 0.0034 Left 74 18/20 0.0007 75 0.0001 Patients Right 64 4/5 ns 64 0.043 with local arthritis Left 65 6/6 0.016 66 0.028 Patients Right 83 11/15 ns 82 0.044 without local Left 77 12/14 0.006 78 0.0012 arthritis
35 Figure 3. Isometric muscle strength in ankle dorsiflexors
Ankle dorsiflexors
200
patient right patient left 100 control right control left
strength % of expected % of strength 0 1 2 3 4 5 6 7 8 9 1011121314151617181920 patient and control number
Ankle dorsiflexors
200
right 100 left strength % expected of strength 0 with local arthritis without local arthritis
36 Table 6. Isometric muscle strength in ankle dorsiflexors
Isometric Compared to reference values Compared to matched strength controls Ankle Percentage Number Significance Percentage Significance dorsiflexors of expected below of control value expected group’s value value All patients Right 94 15/20 0.021 89 0.012 Left 93 12/20 ns 96 ns Patients Right 79 6/6 0.016 80 0.028 with local Left 78 7/7 0.008 84 0.028 arthritis Patients Right 102 9/14 ns 93 ns without local Left 103 5/13 ns 103 ns arthritis
37 Figure 4. Isometric muscle strength in elbow flexors
Elbow flexors
200
patient right patient left 100 control right control left
strength % of expected 0 1 2 3 4 5 6 7 8 9 1011121314151617181920 patient and control number
Elbow flexors
200
right 100 left strength % ofstrength expected % 0 with local arthritis without local arthritis
38 Table 7. Isometric muscle strength in elbow flexors
Isometric Compared to reference values Compared to matched strength controls Elbow Percentage Number Significance Percentage Significance flexors of expected below of control value expected group’s value value All patients Right 83 16/20 0.006 77 0.0001 Left 86 18/20 0.0002 81 0.0013 Patients Right 64 2/3 ns 68 ns with local Left 62 2/2 ns 66 ns arthritis Patients Right 86 14/17 0.006 78 0.0003 without local Left 89 16/18 0.0007 83 0.003 arthritis
39 Figure 5. Isometric muscle strength in wrist dorsiflexors
Wrist dorsiflexors
200
patient right patient left 100 control right control left
strength % expected of strength 0 1 2 3 4 5 6 7 8 9 1011121314151617181920 patient and control number
Wrist dorsiflexors
200
right 100 left strength % of expectedstrength % 0 with local arthritis without local arthritis
40 Table 8. Isometric muscle strength in wrist dorsiflexors
Isometric Compared to reference values Compared to matched strength controls Wrist Percentage Number Significance Percentage Significance dorsiflexors of expected below of control value expected group’s value value All patients Right 82 13/20 ns 75 0.002 Left 74 16/20 0.006 76 0.002 Patients Right 47 5/6 ns 43 0.046 with local Left 43 6/6 0.016 45 0.028 arthritis Patients Right 97 8/14 ns 88 0.03 without local Left 88 10/14 ns 89 0.04 arthritis
41 Figure 6. Isokinetic muscle strength in ankle dorsiflexors
Isokinetic strength in ankle dorsiflexors
200
patient right 100 patient left
strength % expected of strength 0 1 2 3 4 5 6 7 8 9 1011121314151617181920 patient number
Isokinetic strength in ankle dorsiflexors
200
right 100 left strength % ofstrength expected % 0 with local arthritis without local arthritis
42 Figure 7. Isokinetic muscle strength at different angular velocities
Isokinetic strength ankle dorsiflexors
120
100
80 all patients 60 with local arthritis 40 without local arthritis
20 strength % of expected of % strength 0 0 50 100 150 200 250 angular velocity (deg/sec)
Table 9. Isokinetic muscle strength in ankle dorsiflexors
Isokinetic strength Compared to reference values Ankle dorsiflexors Percentage of Number below Significance All velocities expected value expected value All patients Right 89 13/20 ns Left 83 13/20 ns Patients with Right 72 6/7 ns local arthritis Left 70 9/9 0.002 Patients without Right 100 7/13 ns local arthritis Left 97 4/11 ns
43 Figure 8. Handgrip strength
Handgrip strength
200
100 patient right
strength % of expected 0 1 2 3 4 5 6 7 8 9 1011121314151617181920 patient number
Handgrip strength
200
100 right strength % of expected of % strength 0 with local arthritis without local arthritis
44 Table 10. Handgrip strength
Handgrip strength Compared to reference values Percentage of Number below Significance expected value expected value All patients Right 80 17/20 0.002
Patients with Right 56 6/6 0.016 local arthritis
Patients without Right 89 11/14 0.029 local arthritis
45 Figure 9. Non-voluntary muscle strength
Non-voluntary strength
200
100 right
strength % expected of strength 0 1 2 3 4 5 6 7 8 9 1011121314151617181920 patient number
Non-voluntary strength
200
100 right strength % ofstrength expected % 0 with local arthritis without local arthritis
46 Table 11. Non-voluntary muscle strength
Non-voluntary Compared to reference values strength Percentage of Number below Significance expected value expected value All patients Right 91 13/18 0.048
Patients with Right 85 8/8 0.004 local arthritis
Patients without Right 96 5/10 ns local arthritis
47 Figure 10. Quadriceps muscle thickness
Muscle thickness
50 40 patient right 30 patient left
mm 20 control right 10 control left 0 1 2 3 4 5 6 7 8 9 1011121314151617181920 patient and control number
Muscle thickness
200
right 100 left % ofexpected %
0 with local arthritis without local arthritis
48 Table 12. Quadriceps muscle thickness
Quadriceps Compared to reference values Compared to matched muscle controls thickness Percentage Number Significance Percentage Significance of expected below of control value expected group’s value value All patients Right 88 14/20 ns 88 0.003 Left 83 17/20 0.001 85 0.0009 Patients Right 73 5/5 0.031 77 ns with local Left 71 6/6 0.016 75 0.046 arthritis Patients Right 93 9/15 ns 91 0.02 without local Left 89 11/14 0.029 89 0.008 arthritis
Table 13. Muscle strength in healthy controls compared with reference values
Controls Compared with reference values Percentage of Number below Significance expected value expected value Knee extensors Right 100 9/20 ns Left 99 10/20 ns Ankle dorsiflexors Right 105 8/20 ns Left 97 8/20 ns Elbow flexors Right 109 6/20 ns Left 106 9/20 ns Wrist dorsiflexors Right 110 4/20 0.006 Left 98 11/20 ns
Muscle strength was reduced for knee extensors, elbow flexors and wrist dorsiflexors in the JCA/JIA group. The findings were almost the same whether the results were compared to reference values or to matched controls. The reduction was found mainly in patients with arthritis in a joint near the examined muscle. For ankle dorsiflexors the strength was reduced in this group only. The strength in most muscles was about 60–70% of the expected value for
49 patients with local arthritis. This means that the strength is slightly reduced, but probably within the normal range in most patients. For a few patients the strength was more markedly reduced. This is most obvious in patients with arthritis near the examined muscle. For local arthritis the following joints were judged as important: knee and hip for knee extensors, ankle for ankle dorsiflexors, elbow and shoulder for elbow flexors, wrist for wrist dorsiflexors, and wrist and fingers for handgrip strength and non-voluntary strength. In some tests a small reduction of strength was found even in muscles far from an inflamed joint. In ankle dorsiflexors the results were comparable for isometric and isokinetic strength measurement. Isokinetic strength was most reduced at higher angular velocities. Non-voluntary strength was slightly reduced in patients with local arthritis. Muscle thickness was reduced in the whole group, but the reduction was greatest in patients with arthritis in the knee or hip. The results of the current study are in accordance with findings in adults with RA. Hsieh et al [28] found a strength of 80% of normal in the quadriceps muscle in RA patients with minimal knee involvement. In a study by Danneskiold-Samsoe et al [29] on women with RA without knee arthritis, a reduction of knee extensor strength to 85% of that of healthy controls was found. In a group of patients with severe arthritis in the knee joint, Nordesjo et al [67] found a strength in knee extensors of 30–45% of healthy controls. Hakkinen et al [68] found that compared to healthy controls muscle strength in knee extensors was 46% lower and handgrip strength 31% lower in women with recent onset RA. Muscle strength in JCA/JIA has been much less studied. Giannini et al [45] examined muscle strength in JRA and found significantly lower strength in knee extensors compared to healthy children. They found no relationship between muscle strength and measures of articular disease severity. Hedengren et al [46] found no reduction in knee extensor strength in children with JCA compared to healthy children, except for a subgroup in muscles in the lower leg. In the present study, however, muscle strength was more reduced in muscles near inflamed joints. The lowest strength values were measured in children with either polyarticular disease or active arthritis near the examined muscle.
50 Paper II Paper II is a longitudinal and observational study over a two-year period. The aim was to evaluate changes in muscle strength and muscle thickness of knee extensor muscles over time. Knee arthritis is common in JCA/JIA, and this was the case in many of the children in the study group. Isometric strength of knee extensors, muscle thickness of the quadriceps muscle, and a joint severity score of knee and hip were measured repeatedly for two years. Isometric strength was measured with a handheld electronic dynamometer (Myometer®). Muscle thickness was measured by ultrasound imaging at mid-thigh level. The examination was repeated every three months irrespective of symptoms. The results were evaluated in three different ways.
First the relationship between the degree of local arthritis and muscle strength and thickness was analysed by using one mean value for each patient. The mean value (one dot for each patient) of a test is an average over two years. For muscle strength there was a significant relationship between a high arthritis severity score and a reduction in muscle strength (Figure 11). Those patients with the most intensive and long-standing local arthritis had the most weakened muscles. Children without local arthritis had strength close to 100% of the expected value for their age and gender.
51 Figure 11. Relationship between muscle strength in knee extensors and local arthritis severity score
Muscle strength and local articular disease severity score
120
100
80
60
40
20 strength % of expected 0 0123456 local arthritis severity score (units)
52 For muscle thickness the relationship was not significant (Figure 12).
Figure 12. Relationship between thickness of quadriceps muscle and local arthritis severity score
Muscle thickness and local articular disease severity score
140 120 100 80 60 % of expected 40 20 0 0123456 local arthritis severity score (units)
53 Some children with weakened muscle also had thin muscles (Figure 13), but the relationship for the whole patient group was not significant. The strength was more frequently reduced than the muscle thickness. The relationship between quadriceps muscle thickness and knee extensor strength has been studied in healthy adults by Freilich et al [69]. They found a significant relationship between maximum isometric strength in knee extensors and thickness of the quadriceps muscle measured by ultrasound.
Figure 13. The relationship between muscle thickness and strength in knee extensors. One mean value for each patient.
Muscle thickness and muscle strength
120
100
80
60
40
20 strength % of expected
0 0 20 40 60 80 100 120 140 muscle thickness % of expected
54 The second way of analysing the results was to study the relationship between the degree of local arthritis and muscle strength and thickness for each patient. Because some patients improved and others deteriorated during the study, an individual regression line was calculated for those patients who had an obvious change in local arthritis score. Ten children had a clear change in arthritis score (> 2 units) during the period. The slope of the regression line is a measure of the relationship between arthritis severity and strength or muscle thickness.
For eight of ten patients there was a significant negative slope of the regression line for muscle strength (Figure 14), implying that muscle weakness is correlated to the degree of local joint inflammation. The mean slope was significantly negative.
Figure 14. Relationship between local arthritis severity score and muscle strength in 10 patients with variation in arthritis severity score. The thick line is the mean of 10 patients.
Muscle strength and local articular disease severity score
120
100
80
60
40
strength % of expected 20
0 024681012 local arthritis severity score (units)
55 For all ten patients there was a significant negative slope of the regression line for muscle thickness (Figure 15). The mean slope was significantly negative. Muscle hypotrophy is therefore correlated to the degree of local joint inflammation.
Figure 15. Relationship between muscle thickness and local arthritis severity score in 10 patients with variation in arthritis severity score. The thick line is the mean of 10 patients.
Muscle thickness and local articular disease severity score
120
100
80
60
40 % of expected 20
0 024681012 local arthritis severity score (units)
56 The third way of analysing the results is to study patterns in the individual patients’ results. Some patterns of the results are shown in the examples below (Figure 16–22).
57 Figure 16. Patient No. 4
400 strength (N)
350
300
250
200
150
100
50
0 12,5 13 13,5 14 14,5 15
muscle thickness (mm) 40
35
30
25
20
15
10
5
0 12,5 13 13,5 14 14,5 15
20 local arthritis severity score (units) 18 16 14 12 10 8 6 4 2 0 12,5 13 13,5 14 14,5 15 age (years)
58 Patient No. 4 (Figure 16) is a girl with severe polyarthritis whose disease worsened during the study. She had arthritis in many joints including the left knee and hip. The figure shows left knee extensor strength and thickness. Strength and thickness decreased both in absolute terms and relative to reference values (lines: mean and ± 2 SD). The local arthritis continued despite all efforts to improve the disease. There was no improvement of strength or muscle thickness during the study period.
59 Figure 17. Patient No. 11
strength (N) 300
250
200
150
100
50
0 9,5 10 10,5 11 11,5 12 12,5
45 muscle thickness (mm)
40
35 30
25 20
15 10
5
0 9,5 10 10,5 11 11,5 12 12,5
20 local arthritis severity score (units) 18 16 14 12 10 8 6 4 2 0 9,5 10 10,5 11 11,5 12 12,5 age (years)
60 Patient No. 11 (Figure 17) is a boy with oligoarthritis and arthritis in the right knee and left hip. The figure shows the results for the right leg. During the first year there was a deterioration despite treatment. During the second year the patient improved and both strength and muscle thickness increased when the intensity of the knee arthritis decreased.
61 Figure 18. Patient No. 12
450 strength (N) 400 350 300
250 right 200 left 150 100 50 0 10,5 11 11,5 12 12,5 13 13,5
muscle thickness (mm) 45 40 35 30
25 right 20 left 15 10 5 0 10,5 11 11,5 12 12,5 13 13,5
local arthritis severity score (units) 12
10
8
6 left
4
2
0 10,5 11 11,5 12 12,5 13 13,5 age (years)
62 Patient No. 12 (Figure 18) is a boy who has had low-active monoarthritis in his left knee for many years, resulting in overgrowth of the leg. The thigh muscle in the left leg was visibly thinner than in the right leg. Muscle thickness was lower in the left leg, but muscle strength was normal without difference between left and right legs.
63 Figure 19. Patient No. 14
strength (N) 600
500
400
300
200
100
0 14 14,5 15 15,5 16
muscle thickness 50 45 40 35 30 25 20 15 10 5 0 14 14,5 15 15,5 16
12 local arthritis severity score (units) 10
8
6
4
2
0 14 14,5 15 15,5 16 age (years)
64 Patient No. 14 (Figure 19) is a boy with oligoarthritis who developed arthritis in his right knee in the middle of the study period. Muscle strength and thickness decreased at the same time, but strength was much more reduced than muscle thickness.
65 Figure 20. Patient No. 19
700 strength (N)
600
500
400
300
200
100
0 16 16,5 17 17,5 18 18,5
50 muscle thickness (mm) 45 40 35 30 25 20 15 10 5 0 16 16,5 17 17,5 18 18,5
20 local arthritis severity score (units) 18 16 14 12 10 8 6 4 2 0 16 16,5 17 17,5 18 18,5 age (years)
66 Figure 21. Ultrasound images from patient No. 19 and the matched healthy control
Patient No. 19 Age-matched control to patient Muscle thickness 22 mm No. 19 Muscle thickness 38 mm
Patient No. 19 (Figure 20–21) is a boy with severe polyarthritis, including chronic hip and knee arthritis in his right leg, shown here. Both strength and muscle thickness were constantly reduced over the whole study period.
67 Figure 22. Patient No. 8
600 strength (N)
500
400
300
200
100
0 15,5 16 16,5 17 17,5 18
muscle thickness (mm) 40
35
30
25
20
15
10
5
0 15,5 16 16,5 17 17,5 18
local arthritis severity score 14 (units)
12
10
8
6
4
2
0 15,5 16 16,5 17 17,5 18 age (years)
68 Patient No. 8 (Figure 22) is a girl with polyarthritis, including right hip and knee. She had reduced muscle strength but normal muscle thickness. There was no obvious change in muscle strength or thickness related to the increase in local arthritis severity score.
The results of the present study have shown that there is a relationship between strength, muscle thickness and intensity of local arthritis, both during improvement and deterioration. For some patients muscle function deteriorated despite treatment. In a study by Geborek et al [70], an improvement of knee extensor strength was found after treatment of knee arthritis in adults with intra-articular corticosteroid injections.
69 Paper III Paper III is a descriptive longitudinal study chiefly focusing on hand function and changes over time during the two-year follow-up. Isometric strength in wrist dorsiflexors was measured every three months over two years. Handgrip strength was measured three times one year apart. The reference values for handgrip strength are from nine years of age, so the two youngest patients were not included in this evaluation. Strength was evaluated in relation to the local arthritis severity score and subgroup of disease. The slope of the regression line for the variables age and strength was used to evaluate changes over time. A negative slope indicates a decrease in muscle strength, i.e. a muscle weakening. Low strength was defined as values below -2 SD from the mean of the reference value. The results are shown schematically in Figure 23 and 24.
70 Figure 23. Results from strength measurements in wrist dorsiflexors during two years
Wrist dorsiflexors
Strength
Patient nr
+2SD
3
1 14 17 16 mean 13 7 12 2 15 10 11 5 6 -2SD 9 20 8 19 4 18
start end
71 Figure 24. Results from measurement of handgrip strength during two years
Handgrip strength
Strength
Patient nr
+2SD
3
12
10 7 mean 5 13 9 14 6 17 15 11 20 -2SD
16 18 4 8 19
start end
Most of the patients showed normal strength in wrist dorsiflexors and hands without change during the two years. Four children had a significant drop in muscle strength, and four had a constant low strength.
There was a significantly increased risk of low or decreasing strength in patients with polyarthritis or active local arthritis in the hand or wrist. In a study by Jones et al [71], significantly impaired hand function was found in adult RA. Improvement in grip strength
72 correlated with improvement in active joint count. Early hand involvement in JRA has been shown by Ruperto et al [72] to be a strong predictor of poor outcome.
The results of the nerve conduction velocity studies in the upper extremity were normal in all cases. No changes appeared during follow-up. Nerve conduction studies have earlier been performed in JRA by Puusa et al [73], who neither found signs of neuropathy.
73 Paper IV In this cross-sectional study, muscle function was evaluated in relation to findings in muscle biopsies. Only 15 of the 20 patients initially recruited were willing to participate in this part of the study. Muscle biopsies were taken from the anterior tibial muscle. Before the biopsy procedure isometric and isokinetic strength were measured in ankle dorsiflexors on the same side according to the schedule previously described. Muscle biopsies were analysed in three different ways. First, a standard histopathological examination was performed. Second, an immunohistochemical examination was carried out to evaluate any abnormal expression of inflammatory markers. Third, muscle fibre types and areas were measured. Because of sparse amount of muscle tissue, this could not be performed for two patients. The results were compared with muscle biopsies obtained from the gastrocnemius muscle in healthy young adults. The methods and evaluations were identical.
Minor morphological changes such as increased variability of fibre diameter and presence of some atrophic fibres were found in the majority of patients (Table 14). Such unspecific findings are sometimes found in healthy people, but the frequency was significantly higher in the patients compared to the controls. The presence of cellular infiltrates is not a normal finding in muscle biopsies. In two of the patients (8 and 15) this was found (Figure 25). The infiltrates were small, sparse and perivascular, and may be a sign of mild inflammation in the muscle, though there was no obvious myositis. The expression of MHC class II was found in four patients, but not in any of the controls. This may be a sign of abnormal immunological activity in the muscle.
Table 14. Results from muscle biopsies
Histopathological and immunohistochemical findings in muscle biopsies Minimal Cell infiltrates MHC class I MHC class II MAC morphological changes Patients n = 15 11/15 2/15 1/15 4/15 2/15 Controls n = 33 7/33 0/33 2/33 0/33 1/33 p-value 0.046 ns 0.014 ns
74 Figure 25. Image showing perivascular cell infiltrates in the muscle
Muscle strength was significantly reduced for the whole group; three patients had muscle strength below -2SD of the reference values (Table 15).
Table 15. Muscle strength in ankle dorsiflexors
Muscle strength in ankle dorsiflexors (% of expected value) Isometric Isokinetic (30 deg/sec) Patients n = 15 86% (3 patients < -2SD) 82% (1 patient < -2SD) p-value 0.018 0.008
75 The mean area of fibre types did not differ significantly from the control group (Table 16, Figure 26).
Table 16. Results from fibre type analysis
Muscle fibre types and areas Type I fibres Type IIA fibres Type IIB fibres Mean area type I/IIA % Mean % Mean % Mean % area µm² area µm² area µm² Patients 75 3158 20 4520 5 3483 77 n = 13 Controls 53 3620 33 3758 14 3681 99 n = 33 p-value ns ns ns 0.0014
Figure 26. The mean area of different fibre types in patients and controls
area 10000 mean area of type IIA fibres 9000 mean area of mean area of type I fibres 8000 type IIB fibres
7000
6000
5000
4000
3000 ns ns ns 2000 1000 patients controls patients controls patients controls
0
76 The relationship between the mean area of type I fibres and the mean area of type IIA fibres differed from the control group (Figure 27). Most patients had a larger area of type IIA fibres than type I fibres. It is known from studies in healthy people that fibre type distribution and size vary in different parts of the muscle [74, 75]. The biopsies in the current study were obtained from patients and controls using the same technique.
Figure 27. The relationship between the mean fibre area of different fibre types
% 200 180 type I/Type IIA area type IIA/Type IIB area 160 140 120 100 80
60 p=0.0014 ns 40 patients controls patients controls 20 0
77 Figure 28. Image from biopsy taken from patient 14 (in paper IV). Type I fibres are light and type II fibres dark.
There was a significant correlation between mean muscle fibre area and isometric strength. There were no significant correlations between morphological changes in the biopsy and strength, or relative areas of type I and type IIA fibres and strength. The mean muscle fibre area was not significantly affected by the presence of active local arthritis, as might have been assumed from the other studies (papers I–III). The study group is small, however, and the conclusions therefore somewhat uncertain.
78 A nerve conduction study was performed on nerves in the leg. The results were normal, as they also were in the upper extremity.
Neuromuscular complications occur in adults with RA [76]. Muscle biopsies have shown inflammation and muscle fibre degeneration [31]. Miro et al [32] examined muscle biopsies from RA patients. They found inflammation in the muscle in 43% of patients with muscular symptoms, mainly weakness, atrophy and pain. In a study by Halla et al [33], signs of inflammation were found in muscles both in patients with active and inactive RA. Myopathy may also occur as a complication of treatment with steroids, chloroquine and d-penicillamine in RA [32, 77-79]. Electrophysiological studies have shown signs of neuropathy (distal symmetric neuropathy, vasculitic neuropathy and compression neuropathy), sometimes subclinically in adult RA [35, 36, 38, 80, 81]. Several studies on adult RA have found muscle fibre atrophy, especially affecting type II fibres [31-33, 82]. Muscle weakness and atrophy sometimes develops in RA patients without any obvious reason. Inactivity due to the disease is one probable cause. Muscle adaptation in response to inactivity has been studied by Berg et al [18]. They found that in healthy persons after six weeks of bed rest, knee extensor strength was decreased by 24%, quadriceps muscle cross- sectional area decreased by 13%, and mean muscle fibre area decreased by 17%. The significant change in muscle fibre area was for type I fibres. The mean area of type IIA and type IIB fibres did not change significantly. The fibre types did not change. The change in strength was greater than changes in fibre area and muscle cross-sectional area. This was further examined in an experimental setting by Larsson et al [83], where isolated human muscle fibres were analysed. The force-generating capacity of muscle fibres decreased by about 40% after 6 weeks of bed rest. Their content of contractile myofibrillar proteins decreased during the same time. Localised atrophy of muscles near an active arthritis may be caused by what is termed reflex inhibition [22, 23]. Joint pain or distension may inhibit local muscle activation and induce “immobilisation” of the muscle. The result on the cellular level may be the same as in experimental unloading. The expression of inflammatory markers MHC class I and class II has been found in muscles of adult RA patients [54] and in myositis [64]. Expression of MAC has been found in juvenile dermatomyositis [56]. No published study on these markers in muscles of children with JIA has been found.
79 80 Summary of results
Table 17 summarises the overall results for all measurements of strength and muscle thickness over two years.
Table 17. Overall results from all strength measurements and muscle thickness during two years
Patient Elbow Wrist Knee Ankle Ankle Handgrip Non- Muscle number flexors dorsi- extensors dorsi- dorsi- strength voluntary thickness (isometric) flexors (isometric) flexors flexors strength (quadri- (isometric) (isometric) (isokinetic) ceps) 1 N N N N N L Not done N 2 N N N N N L N N 3 N N N N N N N N 4 L L L L L L N L 5 N N N N N N N N 6 N SL N N N N N N 7 N N SL N N N N N 8 SL SL SL N SL L N N 9 N N N N N N N N 10 N N N N N N N N 11 SL N L N N N N N 12 N N N N N N N N 13 N N N N N N N N 14 N N SL N N N N N 15 N N N N N N N N 16 L SL SL N N N N L 17 N N N N N N N N 18 L L N N N L N N 19 L L L L L L N L 20 SL L N SL L N N N
N: normal (most values during two years within ± 2 SD of the mean of the reference values) L: low (most values during two years < -2 SD) SL: some low (some values during two years < -2 SD)
Two patients (No. 4 and 19) had very low values in nearly all tests. Clinically they had the most severe disease of these 20 patients. They had polyarthritis and for periods required a wheelchair. Nine patients had results within normal limits in all tests. Three had normal results in almost all tests. Six patients had low values in some of the muscle groups, all of which probably were due to localised arthritis.
81 82 General considerations
There are a number of methodological problems with this type of study.
The study is observational without evaluation of the effect of treatment. This means that there are no points in time where the results before and after any measures taken can be evaluated. Any impairment of the patients was counteracted by more intensive treatment, which probably reduced the impact on muscle function. Some patients improved and others deteriorated during the follow-up.
The patient group is very heterogeneous, and the disease probably includes arthritis with different aetiologies and prognoses. The spectrum of the disease is extensive. Some patients have isolated arthritis in a single joint which hardly influences the activity of their daily lives and is relatively easy to treat; others have severe polyarthritis with destruction of joints and which seems resistant to all treatment.
The patient group is small. It is not a common disease, and the youngest patients are difficult to examine with some of these methods. Not all suitable patients are willing to participate in this type of long-time study.
There are problems with all types of strength measurements. The results are highly dependent on the person’s capacity to perform a maximal muscle contraction, as well as the patients’ motivation, mood and cooperation and the examiner’s ability and willingness to push the patient. There is variability between investigators and results are very dependent on the methods used.
There are special problems in evaluating strength in growing children. First, muscle volume and strength increase with age. Second, the lever, i.e. the length of the limb, increases during growth. The longer lever makes the torque greater. The reference values for strength measurement using these methods are originally related to age. Body size at a specific age can vary a considerably, particularly in the accelerated growth at puberty. This makes the “normal” strength span, i.e. ± 2 SD, quite wide for some ages. For comparisons between patients of different ages and gender, it is sometimes better to relate the measured value to the
83 mean of the reference group and express strength as a percentage of the “expected” value, particularly when changes over time are evaluated. The strength value of one person would otherwise change from, for instance from -2 SD to -1 SD, simply because of the variability in muscle strength in the reference group, even if strength deviation from the mean of the reference value were constant. In the current study a matched control group was also used. The controls were, however, a convenience sample and not randomly selected.
When measuring strength in joint disorders, one must take the influence of pain into account. Pain is a component of inflammation, and many people with arthritis have joint or muscle pain. If the pain is associated with movements of the joint, it will probably influence the results of strength measurement. In the current study most measurements were carried out using isometric methods, where minimal movement of the joint is required. Intensive joint pain would nevertheless reduce the effort to perform a maximal muscle contraction. In the study group, pain on measurement was not commonly reported. Pain on movement of a joint is one item measured in the arthritis severity score used in the study.
The main method of strength evaluation in this study, isometric strength measurement, was chosen because it is a simple and convenient method in clinical practice. The handheld dynamometer is easy to carry and can be used for many different muscle groups and in any examination room. It has been used in other studies [84] and was found to be sensitive to changes in muscle strength. The more sophisticated method of isokinetic strength measurement has many advantages, but the equipment is not so easy to handle and the test is more time consuming.
The ultrasound imaging method used for measurement of muscle thickness is also relatively simple to perform, but does not give as detailed information on muscle volume as MRI or a CT scan. Ultrasound is, however, harmless and can be repeated many times.
The main problem of the muscle biopsy study is the small number of patients and the lack of an age-matched control group. Only 15 of the 20 patients were willing to participate in the muscle biopsy procedure. The group was heterogeneous with different ages, genders and disease subgroups. It was not considered ethical to perform muscle biopsies on healthy children for research purposes. The control group for muscle biopsies was young adults, most of them women. The muscle biopsy was taken from the gastrocnemius muscle in the controls
84 and from the anterior tibial muscle in patients. This may also explain some of the differences between the groups.
85 86 Main conclusions
Children and teenagers with JCA/JIA have as a group reduced muscle strength and muscle thickness compared to healthy people. For most, the strength is only slightly lower than expected, but a few have obvious muscle weakness. This is most apparent in patients with severe polyarthritis where the weakness appears to be widespread. Patients with isolated arthritis may also have greatly reduced strength and thickness of muscles near the inflamed joint. There is a risk of decreasing strength in patients with polyarthritis and in muscles near an active arthritis.
Minor changes are common in muscle biopsies, and findings may indicate immunological activity in the muscles.
Atrophy of type II fibres, as in adult RA, was not found in JIA.
Neuropathy may not be a feature of JIA.
87 88 Acknowledgements
To all of you who have helped me in my work, from beginning to end, I would like to express my gratitude. There are many people, not all named individually, who have supported me over the years in my research. I would like to thank you all:
Eva Svanborg, my supervisor, who encouraged and pushed me to finish this work.
Per Sandstedt, my initial supervisor, who inspired me to start this research project many years ago. You never lost hope.
The late Eva Bäckman, my initial co-supervisor, who introduced me to the art of strength measurement in children.
Magnus Vrethem and Nicola Reiser, my colleagues and friends, for help, encouragement and for doing my clinical work when I was writing my thesis.
All the staff at the Department of Clinical Neurophysiology: Karin, Ludka, Inga-Britt, Gunnel, Maria, Maggan, Suzanne, Carina and Per for sharing my daily work, and for skilful help with the examination of the children in this study.
Björn Lindvall, co-author and friend, who knows everything about muscle histopathology.
Lisbeth and Gunvor at the Neuromuscular Unit, for skilful work with the muscle biopsies.
My colleagues and the staff at the Department of Paediatrics where this study started in the late eighties.
Margareta Resjö who taught me to carry out the ultrasound examinations.
All the children and young people, both patients and controls, who participated in this study, and their parents.
Lastly, but most important, I would like to thank my family.
89 90 References
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