Myasthenia gravis associated with carcinoma of the thymus. A report of three cases

INTRODUCTION: Although the association between benign neoplasias of the thymus and myasthenia gravis is well known, with greater predominance of squamous thymomas over other histological types, carcinoma of the thymus is only exceptionally associated with auto immune disorders. CASE REPORTS: We present three patients with myasthenia gravis associated with carcinoma of the thymus. They were three men aged between 38 and 73 years. Clinical features of myasthenia were generalized in two cases and ocular only in the third. Antireceptor antibodies to acetylcholine and anti striped muscle antibodies were present in all three patients. Repetitive stimulation was abnormal in two of the three cases. On CAT of the thorax there was a tumour of the thymus with the radiological characteristics of a benign thymoma in two of the patients and data suggesting an invasive thymoma in the third. In all three cases the diagnosis of carcinoma of the thymus was made on the post operative histological findings. CONCLUSIONS: The association of carcinoma of the thymus with myasthenia gravis in our series of cases was probably due to chance. We consider that this association is exceptional since the histological characteristics of carcinoma of the thymus do not favour the development of auto immunity.