[A case of dermatomyositis associated with thymic abnormalities].

A case of dermatomyositis (DM) associated with thymic cyst with lymphoid follicle formations has been reported. A 57-year-old man developed polyarthralgia, muscle weakness, heliotrope rash and Gottron's sign. Laboratory findings showed elevated values of creatine-phosphokinase, aldolase and transaminase. He was diagnosed as DM and was treated with prednisolone 50 mg/day. Muscle weakness was improved immediately, although rash persisted unchangeably. He was examined for coexistence of malignant tumor which had been reported frequently as associated with DM. Enlargement of thymus was found by computer tomography and then thymectomy was performed. In his thymus, lymphoid follicle formations, which are as often encountered in other autoimmune diseases, were found. So far, the beneficial effect of thymectomy on the improvement of immunological abnormalities not only in patients with myasthenia gravis but also in patients with other autoimmune diseases has been recognized. In this case, intractable rash in DM improved after thymectomy. Further study needs to clarify the relationships between DM and thymic abnormalities.