[A patient with giant cell myocarditis and myositis associated with thymoma and myasthenia gravis].

We report a 62-year-old man with giant cell myocarditis and myositis associated with thymoma and myasthenia gravis (MG). He was diagnosed as having MG and invasive thymoma at the age of 45. After he had a myasthenic crisis at the age of 61, tacrolimus was indicated in order to improve his neurological symptoms, in addition to glucocorticoid. Three months later, he was readmitted to our hospital complaining of general fatigue and dyspnea. Serum level of creatine phosphokinase (9,835IU/L) and myocardium-derived troponin T (3.24 ng/mL) were elevated, and the ECG showed atrioventricular dissociation and accelerated idioventricular rhythm. In spite of glucocorticoid pulse therapies and high-dose immunoglobulin therapies, he died of cardiac failure within a few days. Autopsy was done, and histological examination of the myocardium and the skeletal muscle showed massive necrosis with infiltration of inflammatory cells including giant cells. These findings constituted giant cell myocarditis and myositis. Although it has been suggested that myocardial disorders can often occur in patients with thymoma and/or MG, the mechanism involved is still unknown. This report may provide new knowledge about the pathophysiology of giant cell myocarditis and myositis associated with thymoma and MG.