A case of enlargement of the right atrium associated with myositis detectedby muscle ultrasonography

A 45-year-old woman was admitted because of general malaise. Analysis of her family history revealed that one of her older sisters had died of ulcerative colitis, another sister had systemic lupus erythematosus, and her elder brother had Behcet's disease. Electrocardiography demonstrated atrial fibrillation associated with marked dilation of the right atrium. Ultrasonography of the biceps brachii showed a marked myopathic pattern. A biopsy specimen obtained from the biceps brachii, revealed degeneration and necrosis of the muscle fibers, interstitial infiltration of monocytes, and perivascular infiltration of inflammatory cells. Magnetic resonance imaging of the heart showed marked dilation of the right atrium, as well as diffuse high-intensity areas in the left ventricle in T2-weighted images.We diagnosed the patient as having generalized myositis associated with myocarditis, and administered steroid therapy. One year later, the patient is still receiving steroid therapy and showing continuous improvement of her symptoms. If a patient shows enlargement of one of the cardiac atria or ventricles, the possibility of cardiac or systemic myositis should be considered. In such cases, skeletal muscle ultrasonography may be a useful non-invasive modality for differential diagnosis.