Myasthenia gravis as an autoimmune disease: clinical aspects

Multiple sclerosis associated with defects in neuromuscular transmission

Three patients with multiple sclerosis characterized by exacerbations and remissions of nervous system signs and symptoms disseminated in time and space also had the kind of easy fatiguability seen in myasthenia gravis. In each case abnormal decrements to repetitive stimulation were electromyographically demonstrated and treatment with ephedrine or anticholinesterase drugs increased the patient's functional capacity while improving the electromyographic abnormality. The suggestion is that these patients represent an overlap syndrome, analogous to the overlap syndrome existing between systemic lupus erythematosus and rheumatoid arthritis where clinical and laboratory features of two diseases coexist in the same patient at the same time. Presumably some patients with multiple sclerosis have deficient production of acetylcholine, just like patients with myasthenia, and treatment with agents useful in myasthenia is able partially to correct the symptoms caused by the deficiency. The cases illustrate how in neurology greater attention to the more immediate cause of clinical symptoms, in the absence of a known aetiology, may result in benefit to the patients.

Serum enzyme levels in patients with myasthenia gravis afte aerobic and ischaemic exercise

This study was designed to test the hypothesis that there is a myopathic component in myasthenia gravis. Serum enzyme analyses and lactate and pyruvate assays were undertaken before and after exercise in order to detect possible leakage from defective muscle membrane. A patient and a control group were exercised under (1) aerobic conditions, (2) ischaemic conditions, and (3) aerobic conditions under the influence of edrophonium chloride. The patient group showed a higher resting level of lactate in the aerobic state than did the controls. In addition, the average change in SGOT values in the patient group after one minute of aerobic exercise under the influence of edrophonium chloride exceeded that of the control group. Both these findings suggest possible leakage of enzyme and metabolite from the myasthenic muscle due to a membrane defect and support the hypothesis that there may be a myopathic component in myasthenia gravis. However, the two groups showed no significant differences in CPK values, which are often elevated in primary muscle diseases.

Thyrotoxic muscle disease

Evidence suggests that most hyperthyroid patients have a proximal myopathy. The more severe this is the more frequently are distal muscles, and ultimately, bulbar muscles involved. Probably acute thyrotoxic myopathy or encephalopathy supervenes on a previous chronic background or occurs concurrently with skeletal muscle involvement. Using careful electromyographic techniques evidence of myopathy may be found in most thyrotoxics; it disappears with adequate treatment of the primary disease.

Myasthenia gravis and periodic paralysis are also associated with thyrotoxicosis and their differentiation is discussed. Infiltrative ophthalmopathy is not related to the effects of excess thyroid hormone, but is possibly due to EPS working in conjunction with LATS.