[Giant-cell myocarditis without a symptom of heart failure seen in a patient with myasthenia gravis and concurrent Hashimoto's disease].

A 69-year-old Japanese woman initially noticed difficulty in squatting in the last two years, followed by nasal voice, fatiguability in mastication, and blepharoptosis. On admission to our hospital, in addition to these neurological findings, we detected ectopic arrhythmia and Levine II systolic murmur at the apex region, without any subjective symptoms. The serum titer of anti-acetylcholine receptor antibody was elevated to 28 nmol/l (normal: < 0.2), and she responded to repetitive nerve stimulation at a frequency of 3 Hz showing 13% waning, she had positive test for edrophonium administration, and was diagnosed as having myasthenia gravis (MG). There was no thymoma by radiographic examination. She also had Hashimoto's disease confirmed by the laboratory findings. Chest X-p revealed dilatation of the heart, and 24-hour Holter ECG revealed non-sustained ventricular tachcardia (VT). Ventriculography revealed prominent dilatation of the left ventricle and diffuse hypokinetic ventricular wall motility. Endomyocardial biopsy revealed muscle fiber degeneration, cellular infiltration, and scattered multinucleated giant cells, confirming a diagnosis of giant cell myocarditis (GCM). Quadriceps muscle biopsy revealed a small number of muscle fibers with giant nuclei, but no giant cells were seen. Immunological study revealed elevation of CD4/CD8 ratio and memory CD4 cells. Antibody to anti-cardiac and anti-striate muscle were strongly positive in the serum. Four months later, she developed dyspnea on effort and hypoxia, accompanied by severe bradycardia leading to sinus arrest. For acute cardiac deterioration, steroid pulse therapy was started followed by oral predonisolone and azathioprine, which aggravated myasthenic symptoms. The patient was ventilated for respiratory hypercapnia. During immunoabsobent therapy, she developed VT which caused a cardiac arrest, leading to fatal outcome. In case of MG, especially overlapped with other autoimmune diseases, evaluation of cardiac function should be conducted to detect GCM.