Myasthenia Gravis

Postgrad Med J: first published as 10.1136/pgmj.41.476.356 on 1 June 1965. Downloaded from POSTGRAD. MED. J. (1965), 41, 356 MYASTHENIA GRAVIS I. T. DRAPER, M.R.C.P.E. Neurological Unit, Northern General Hospital, Edinburgh. Definition immune mechanism has been postulated as an MYASTHENIA GRAVIS is a disorder of neuro- atiological factor in the causation of these muscular conduction. It is characterised disorders and it may be that the myasthenic clinically by an excessive degree of weakness patient is genetically predisposed to his disease which develops in the affected muscles during (Simpson, 1960). sustained or repeated contraction. In the early stages of the illness, at least, the strength is Onset partially or fully restored by rest or the The onset of the disease is commonly in- administration of anticholinesterase drugs in sidious, and may at first be neglected by the the appropriate dosage. patient. In such circumstances it is difficult Natural History to establish any precipitating factor. In a Incidence and at onset large number of cases, however, the first age recognised symptoms come on with dramatic The incidence of the disease in the total suddenness. In such a case the precipitating population has been estimated between 1 in factor is more readily identified. This can becopyright. 40,000 (Garland and Clark, 1956) and 1 in a physical or emotional shock, and one may 15 to 20,000 (Eaton, 1958), and it is found be tempted to diagnose hysteria, particularly more commonly in women, in a proportion if the patient is examined after a period of rest 3 to 2 (Schwab and Leland, 1953; Ferguson, when the symptoms and signs have disappeared. Hutchinson and Liversedge, 1955). The stress associated with injury and infection, Although myasthenia gravis may develop at particularly lobar pneumonia, has been related any age, in either sex, it occurs most commonly to the onset of myasthenia gravis. The first between the ages of 15 and 65 years. The in the months of majority of new cases in women appears during symptom may appear early http://pmj.bmj.com/ reproductive life so that the mean age of onset pregnancy, or during the puerperium. In an is 26 years. In men the distribution curve is established case, sudden worsening may appear more symmetrical and the mean age of onset to be precipitated by similar circumstances. is 31 years (Simpson, 1958). The relationship The disease may first be recognised by the of myasthenia gravis to pregnancy and the patient's abnormal response to drugs. The menstrual cycle is considered below. patient with myasthenia gravis is especially occur in sensitive to curare and there may be a failure Progressive myasthenia gravis may to establish normal respiration after surgery on October 2, 2021 by guest. Protected childhood, and a rare, transient form, neonatal when muscle relaxants have been used. There myasthenia is sometimes found in the children is uncertainty about the role of procaine as a born to women with myasthenia. precipitant. I examined an elderly woman Family History with ocular myasthenia, whose first symptoms Several authors have recorded the multiple developed after an operation for cataract, incidence of myasthenia gravis in one family performed under procaine anesthesia. (Oppenheim, 1898; Rothbart, 1937; Teng and Osserman, 1956), but on present evidence this Course of the disease cannot be considered as a familial disease The susceptibility of the affected muscles to (Simpson, 1964). However, a careful scrutiny rapidly increasing weakness or "fatigue" has of the family histories of patients with already been stressed. Unlike normal fatigue myasthenia gravis reveals an unusual incidence myasthenic "fatigue" proceeds to complete of thyroid disease and rheumatoid arthritis. paralysis. Most patients feel stronger in the In common with myasthenia gravis, an auto- morning and fatigue more readily in the Postgrad Med J: first published as 10.1136/pgmj.41.476.356 on 1 June 1965. Downloaded from June, 1965 DRAPER: Myasthenia Gravis 357 12-20o '9090 4-8 60-70 copyright. 1-4.u: 50' 60 ONSET TOTAL FIG. 1.-Percentages of cases in which various muscle groups are affected at the onset (left of key) and at some time during the illness (right of key). http://pmj.bmj.com/ Simpson, J. A. (1960). Scot. Med. J., 5, 419. afternoon or evening. Paradoxically, some some improvement during the later months patients feel at their worst in the morning (Viets, Schwab and Brazier, 1942). Relapse improving as the day goes on. A comparable may occur during the puerperium (Fraser and situation exists in that some patients feel that Turner, 1953). There is often a transient can "work off" weakness but it is uncertain they incipient by premenstrual worsening, on October 2, 2021 by guest. Protected active effort. Apart from physical effort there whether this represents a true physical impair- are environmental factors which influence the ment. Objective evidence of a disturbance course of the illness. Extremes of temperature associated with menstruation seemed to be cause an increase in weakness: the very local provided by Schrire (1959) who described a increase in temperature experienced in a hot reduction in the excretion of pregnandiol by bath may exaggerate the weakness. One or two non-pregnant myasthenic women, but Simpson patients have described a worsening of ocular (1964) was unable to confirm these findings. symptoms in bright sunshine perhaps provoked The patient's emotional state plays a great by actively screwing up their eyes. part in determining his response. Enthusiasm Reference has been made to the higher and confidence in the patient and the attending incidence of myasthenia gravis in women of physician auger well in the management of the reproductive age and the fluctuations experi- disease. enced during pregnancy and the puerperium. While minor fluctuations in the severity of The likelihood of deterioration is greatest the disease are common, complete remission is during the first trimester of pregnancy, with relatively rare. The most marked variations in Postgrad Med J: first published as 10.1136/pgmj.41.476.356 on 1 June 1965. Downloaded from 358 POSTGRADUATE MEDICAL JOURNAL June, 1965 severity occur within the first seven years of Permanent "myopathic" changes may develop the illness and the risk of death, directly in affected muscles. Simpson recorded myo- attributable to the myasthenic process is also pathic changes in 10% of the females and greatest during this period. By the same token 20% of the males in his series (Simpson, 1958). any worthwhile remission is more likely to These changes are most commonly found in occur during the first seven years. It is rare the extra-ocular muscles, the triceps brachii, for a patient to have more than one complete iliopsoas, quadriceps femoris and the tongue. remission. Such changes are uncommon in muscles which After seven years, dramatic changes in the have been affected for only a short time. The state of the disease are uncommon and it is duration of weakness is not the only factor, then said to have become stabilised. Thymec- however, as muscles which have been affected tomy as a treatment for myasthenia gravis is for many years may never show myopathic most likely to be effective if undertaken during responses. When assessing the patient's reaction the pre-stable period (Simpson 1958, 1960). to anticholinesterase drugs, the possibility of permanent changes must be considered so that Distribution of the affected muscles a localised failure of response is not necessarily Myasthenia gravis may affect any voluntary as a result. muscle in the body: the smooth muscles are interpreted negative not affected. It is unusual for all the muscles to be affected at any one time. Characteristically, Clinical features some muscles are severely affected, some more The most outstanding symptom is the slightly, and some not at all. By summarising development of unusual weakness after a short the extent of the disease in a large number of period of effort. patients it is possible to construct a statistical Involvement of the extra-ocular muscles gives distribution of the affected muscles (Fig. 1 rise to diplopia, which may increase gradually, (Simpson, 1960)). or may develop suddenly so that objects appear The muscles around the eyes, the extra-ocular to split or slip to one side. Such symptomscopyright. muscles, the levators of the upper lids and the may occur while the patient is concentrating orbiculares oculi, are most often found to be on close, fine work, and will often be relieved involved. Indeed it is uncommon for a patient by closing the eyes for a few moments or with myasthenia gravis to have no symptoms looking away to a more distant object. When or signs referable to these muscles. A too rigid examining eye movements, the patient's ability adherence to this statement, however, will result to maintain his gaze should be tested. During in some atypical cases remaining undiagnosed. this examination an increasing strabismus may, The muscles of the face, tongue, jaw and develop and nystagmoid jerks are commonly palate, and pharynx are almost as frequently seen. These represent the development ofhttp://pmj.bmj.com/ affected as those around the eyes. These are weakness, with a recovery of strength after a followed by the muscles of the neck, shoulders momentary rest. and pelvic girdle. The peripheral limb muscles, Unilateral ptosis may relieve the patient of muscles of the trunk and respiration are less his diplopia. Ptosis may be seen to develop commonly involved. during the examination and minimal degrees Not infrequently the disease appears to be of ptosis are sometimes compensated by over- limited to one group of muscles, and may action of the frontalis muscle on that side become static. This occurs most commonly in (Fig.

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