To describe a case of MDA5 antibody-positive dermatomyositis (DM) with associated cardiomyopathy, broadening the clinical spectrum of a rare and poorly characterized disease.

Antibodies against melanoma differentiation-associated protein 5 (MDA5) are found in approximately seven percent of DM cases presenting with mild myopathy and aggressive interstitial lung disease (ILD) that portends a poor prognosis. Cardiac involvement in DM is rare, and only two cases have been described with MDA5-positive DM.

A 63-year-old woman was evaluated for muscle weakness, weight loss, and fatigue preceded by severe polyarthralgia and rash. Examination showed proximal weakness in all extremities and distal large fiber sensory loss. Her ankle jerks were absent. She had ulcerations on her fingers and hyperpigmented patches and plaques over her chest, elbows, and finger joints.

Electrodiagnostic testing showed a primary disorder of the muscle without membrane irritability and a mixed sensorimotor polyneuropathy. She had mild myopathic features with rare lymphocytes on muscle biopsy and antibody testing showed elevated MDA5 antibody titer. Her CT chest had findings consistent with ILD.

She developed dyspnea and lower extremity edema, and a pericardial friction rub prompted a cardiac work-up. An echocardiogram showed cardiomyopathy with ejection fraction of 30%, a decline from 70%. Cardiac MRI showed diffuse hypokinesis and nuclear stress test did not show ischemia. She was treated with aggressive diuresis and optimal medical management for heart failure. She also received IVIG, corticosteroids, and cyclophosphamide.

MDA5-positive DM is a rare subtype of inflammatory myopathy known to have multi-system involvement including skin, muscle, and lung with ILD causing significant morbidity and mortality. Our case suggests that severe and life-threatening myocardial involvement can be part of the MDA5-positive DM clinical spectrum and highlights the importance of cardiac evaluation in this patient group.