MYASTHENIA GRAVIS : CLINICAL,SEROLOGICAL AND HISTOLOGICAL STUDIES IN RELATION TO THYMECTOMY

In 10 cases of myasthenia gravis correlative studies were made by means of autoimmune serological tests, electromyography, thymic X-ray examination (pneumomediastinography) and assessment of thymic morphology in relation to the effects of thymectomy (nine cases) and thymic irradiation (one case). The 10 patients were placed in three groups, namely (a) three young females with a non-involuted thymus showing “thymitis” and negative results to serological tests who derived benefit from thymectomy, (b) four older females with thymic atrophy and positive results to serological tests who for the most part gained no benefit from thymectomy, and (c) three males with thymomas and positive results to serological tests who obtained benefit from thymectomy in two instances. The presence of the characteristic autoantibody—the myoid antibody which reacted with thymic myoid cells and skeletal muscle—was helpful in diagnosis but did not appear to be related to neuromuscular block, neither was it of value in predicting the response to thymectomy. Electromyography with the decamethonium test showed, with one exception, the characteristic myasthenic responses irrespective of the patient's age, the presence or absence of myoid antibody, or the nature of the microscopic lesion in the thymus. The radiographic outline of the thymus as determined by pneumomediastinography correlated well with the size and shape of the resected thymus. The typical histological appearance in the thymus of abundant cortex and prominent medullary germinal centres and lymphocytosis was termed “thymitis” ; it was characteristic of the thymus of patients in group (a) and the residual thymus of patients with thymoma in group (c). Our clinical observations could be correlated with experimental studies, indicating that myasthenia gravis is associated with a destructive “autoimmune thymitis”. It is suggested that “thymitis” is associated with the release from the medulla of an uncharacterized humoral agent which causes neuro-muscular block.