Int J Clin Exp Med 2016;9(7):13723-13732 www.ijcem.com /ISSN:1940-5901/IJCEM0023830 Original Article Semi-quantitative assessment of lower limb MRI in dystrophinopathy Qi Bing1, Keyou Hu2, Qingbao Tian2, Zhe Zhao1, Hongrui Shen1, Na Li1, Jing Hu1 1Department of Neuromuscular, The Third Hospital, Hebei Medical University, Shijiazhuang, Hebei Province, People’s Republic of China; 2Department of Public Health, Hebei Medical University, Shijiazhuang City, Hebei Province, People’s Republic of China Received January 12, 2016; Accepted May 24, 2016; Epub July 15, 2016; Published July 30, 2016 Abstract: Dystrophinopathy is a group of inherited muscular disorders, including Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), X-linked dilated cardiomyopathy (XLDCM), and manifesting/non-man- ifesting DMD/BMD carriers, which predominantly affects lower limbs. We studied the clinical and lower limb MRI data to assess muscle preservation and muscle choice of dystrophinopathy. Forty-two patients with dystrophinopa- thy underwent clinical, laboratory, and MRI examinations. Semi-quantitative data of muscle strength and muscu- lar MRI were collected and statistical analyzed. Logistic regression was used to assess MRI scores and clinical variables. MRI changes in thigh were more significant than in lower leg (P < 0.001). In addition, the anterior group was more severe than the posterior group in thigh, whereas in lower leg, the posterior was more severe than the anterior. At thigh level, the vastus lateralis was predominantly involved, and the gracilis was less involved. At lower leg level, the long fibular muscle was more involved than the anterior tibial muscle. BMD patients had similar MRI characteristics as DMD. The logistic regression analysis showed that there are three variables (age, weight, proxi- mal muscle strength) affected thigh muscle injury scores. MRI provides a simple, non-invasive means of detecting subtle, subclinical changes in individual muscles that reflects the progression of dystrophinopathy. The selective muscle involvement observed in lower limb MRI can provide diagnostic evidence for DMD and support the argument to initiate therapy at earlier ages. Keywords: Dystrophinopathy, duchenne muscular dystrophy, becker muscular dystrophy, skeletal muscle biopsy, muscle MRI Introduction progressive myocyte degeneration. Boys with DMD experience progressive muscle weakness Dystrophinopathy is caused by mutations in and wasting that results in wheelchair depen- the DMD gene, which encodes the protein dys- dence in later teenage years, cardiorespiratory trophin, and is located on the X-chromo- compromise, and eventually death during young some (Xp21). The dystrophinopathy spectrum adulthood. BMD has a slower progression and encompasses Duchenne muscular dystrophy a longer life expectancy. BMD patients ambu- (DMD), Becker muscular dystrophy (BMD), X- late independently until at least 16 years of linked dilated cardiomyopathy (XLDCM), which age, with a mean age of 30 years. includes asymptomatic hyper-creatine kinase (CK) emia, cramps, myalgia, and quadriceps Muscle involvement in DMD is characterized by myopathy), XLDCM, and manifesting/non- man- repetitive cycles of injury, inflammation, and ifesting DMD/BMD carriers [1]. DMD is the repair that results in progressive degeneration, most severe dystrophinopathy that begins in necrosis, and regeneration of myocytes by fat early childhood and affects 1 in every 3,500- and connective tissue. One of the hallmarks 4,000 male births. DMD gene mutations lead of DMD is a significant loss in bulk of the pro- to defects or deletion of the protein dystrophin, ximal muscles, including those of the pelvis an important cytoskeletal muscle component. and thighs. To precisely diagnose DMD, the cli- This abnormality results in structural fragility, nician is required to make appropriate judg- membrane permeability, metabolic crisis, and ments regarding the distribution of the affect- Lower limb MRI characteristics in dystrophinopathy Figure 1. Immunofluorescence staining of DMD and BMD patients: Normal control (A-C): normal dystrophin presents on the sarcolemma; DMD (D-F): dystrophin is absent on the sarcolemma; BMD (G-I): decreased dystrophin on the sarcolemma. (Bar = 100 μm). ed skeletal muscles, muscular strength, and fatty tissue infiltration. This progressive fatty capacity. Ultrasound (US) has been used as tissue infiltration and muscle weakness report- a well-established and validated diagnostic edly leads to loss of ambulation between the imaging method for evaluating muscle invo- ages of 8-12 years [4, 5]. lvement, but its application is limited to super- ficial muscle groups because it is difficult to Few pelvis and thigh MRI studies in DMD display deeper structures and multiple muscle patients have shown a characteristic pattern groups that overlap. Computed tomography of fatty infiltration that spares the gracilis, sar- (CT) has also been widely used to evaluate the torius, and semimembranosus muscles [6, 7]. presence and extent of changes in myopathy, However, lower leg muscles frequently show en- but its high radiation dose and limited soft largement known as pseudohypertrophy. Re- tissue contrast makes the application obso- search has indicated that the gastrocnemius lete, particularly in children [2]. MRI provides and soleus muscles are predominantly affect- a high soft tissue contrast, thereby allowing ed [8]. Torriani et al. [9] showed that marked excellent assessment of muscles shape, vol- involvement of peroneal muscles is a charac- ume, and tissue architecture [3]. The inflamma- teristic feature of boys with DMD. In addition, tory changes and repair observed during the increased contractile content in both peroneal initial stages of the disease are followed by muscle and medial gastrocnemius with age are 13724 Int J Clin Exp Med 2016;9(7):13723-13732 Lower limb MRI characteristics in dystrophinopathy suggestive of compensatory hypertrophy [10]. pads to restrict leg movement. T1-weighted Furthermore, the degree of adiposity of the axial images were obtained using the follow- lower leg muscles measured by MRI correlated ing parameters: TE: ranged from 13.9 to 18.6 with clinical manifestation, considered quanti- ms, TR: 500 ms, FOV: 38, 18 sections, 6.0/3.0 tative and objective measures of disease se- mm (thickness/gap). This session lasted for verity. We collected muscle MRI data in the 150 seconds. Next, the T1-weighted axial ima- thigh and lower leg of dystrophinopathy pa- ges of fat suppression were obtained using tients and analyzed the MRI characteristics the same parameters. T2-weighted axial imag- of the lower limb. es were acquired using the following para- meters: 3620/85 ms (TR/TE), 20 sections, Materials and methods 6.0/3.0 mm (thickness/gap), and the T2-wei- ghted axial images of fat suppression were The Research Ethics Committee of the Third acquired with the same parameters. Hospital of Hebei Medical University of China approved this study. Written informed con- For the muscle MRI of the lower limb, sections sent was obtained from each participant’s were generally analyzed within the mid to upper parent or guardian, and each child agreed to section of the thigh and lower leg, because the participate in this study. muscle bulk in this section is greatest and mus- cle abnormalities can be more clearly visual- Participants ized. The muscles listed below were assessed in 4 grades. Forty-two patients with dystrophinopathy (age range 4.0-25.0 years) participated in this Thigh: rectus femoris, vastus medialis, vastus study. Patients included 33 boys with DMD, 7 lateralis, vastus intermedius, semitendinosus, boys with BMD, 1 boy with asymptomatic hy- semimembranous, biceps femoris, gracilis, and perCKemia, and 1 female manifesting carrier adductor magnus. (MC). Dystrophinopathy diagnoses were based on a history of progressive muscle weakness, Lower leg: anterior tibial muscle, extensor digi- physical symptoms, and significantly elevated torum longus, extensor hallucis longus, long serum CK levels. Muscle biopsy showed mus- fibular muscle, caput mediale musculi gastroc- cular dystrophy pathologic changes and there nemii, caput laterale musculi gastrocnemii, and was decreased or absent dystrophin immuno- musculus soleus. histochemical staining on the sarcolemma using the dystrophin-N, -C, and -R antibodies Fatty infiltration of the lower limb musculature (Figure 1). Knee flexion and extension were was graded using a semi-quantitative method, evaluated as proximal strength, whereas an- which entailed consensus scoring by two expe- kle plantar flexion and dorsiflexion were eva- rienced musculoskeletal radiologists blinded to luated as distal strength. The proximal and dis- patient data to minimize bias. At the largest tal lower limb muscle strength was evaluated cross-sectional area of each muscle, we used using the Medical Research Council (MRC) the scale described by Mercuri E et al. [12] as scale, as follows [11]: grade 5, normal strength; follows: Stage 0: Normal appearance; Stage 1: grade 4, slight-to-moderate weakness; grade Numerous discrete areas of increased density 3, muscle can move the joint against gravity less than 30% of the muscle volume; Stage 2: but not against any added resistance; grade 2, Numerous discrete areas of increased density muscle cannot move the joint against gravity with early confluence, 30%-60% of the muscle but only in absence of it; grade 1, a trace of volume; Stage 3: Numerous discrete areas of contraction; and grade