A primary mediastinal Hodgkin's lymphoma with asymptomatic myasthenia gravis: a rare association

Myasthenia gravis (MG) is an autoimmune neuromuscular junction disorder that is frequently associated with other autoimmune diseases. It has been only rarely reported in association with thymic Hodgkin's lymphoma. We report a case of a 22-year-old man who presented with thoracic symptoms. Clinical examination was normal. Simple chest radiography showed a heterogeneous mediastinal mass. Thoracic computed tomography revealed an antero-superior mediastinal mass measuring 6 cm and invading the upper lobe of the left lung with parenchymal micronodules of the left lung and an involvement of mediastinal nodes. In order to consider a diagnosis of thymoma, electromyography was performed despite the fact that the patient was asymptomatic. This exam demonstrated signs specific of MG. After stabilising the MG with symptomatic therapies, surgical intervention was performed. Histological and immunohistochemical findings led to the diagnosis of thymic Hodgkin's lymphoma. The MG regressed completely after surgical removal of the lesion. The patient is currently receiving complementary chemotherapy. An association between asymptomatic MG and thymic Hodgkin's lymphoma has not been documented in the literature, and the present case appears to be the first reported. The pathogenesis of this association remains unknown. Some authors support a genetic origin, while others propose a hypothesis based on immunological studies. The treatment of thymic Hodgkin's lymphoma is based on Cotswold staging system. Nonetheless, MG generally regresses after surgical removal of the thymic lesion.