End-Stage Biventricular Failure from Necrotizing Autoimmune Myopathy

Abstract

Necrotizing autoimmune myopathy is a rare neuromuscular disorder characterized clinically by severe proximal limb muscle weakness and pathologically by necrotic muscle fibers with minimal inflammation. It is often associated with statin therapy, connective tissue diseases, and malignancy. Most have characteristic autoantibodies although a small subset present without myositis-specific autoantibodies. While cardiac involvement is rare, conduction abnormalities, diastolic dysfunction, and wall motion abnormalities have been reported. Severe cardiomyopathy from necrotizing autoimmune myopathy resulting in end-stage biventricular failure is extremely rare without a clear role for guideline-directed medical therapy. A 45-year-old man with hypothyroidism was admitted with several months of worsening proximal muscular weakness. He was found to have new severe biventricular dysfunction with conduction abnormalities during diagnostic work-up. Physical exam was notable for symmetric proximal muscle weakness in upper and lower extremities, sclerodactyly, elevated jugular venous distension, and lower extremity edema. Laboratory testing showed a creatine kinase of 3101 U/L, ANA 1:640, positive RNP antibodies, positive PM/Scl 100 antibodies. Anti-HMGCR antibodies and anti-SRP antibodies were negative. Lower extremity MRI showed diffuse bilateral symmetric myositis around the pelvis consistent with an inflammatory myopathy. EMG suggested irritable myopathy. Left thigh skeletal muscle biopsy showed necrotizing autoimmune myopathy with a paucity of inflammatory cells. Electrocardiogram revealed a right bundle branch block and 1st degree AV block. Frequent atrial and ventricular ectopic beats were seen on telemetry. Transthoracic echocardiogram showed biventricular failure with LVEF 23% and severe global hypokinesis. Cardiac MRI showed patchy foci of delayed subendocardial delayed enhancement. Endomyocardial biopsy did not reveal evidence of lymphocytic infiltration or ongoing myocarditis. Right heart catheterization was notable for elevated biventricular pressures with a cardiac index of 2.18. No obstructive coronary artery disease was seen on coronary angiogram. He was treated with intravenous immunoglobulins, methotrexate, and high-dose prednisone with improvement in proximal weakness. Low-dose spironolactone and lisinopril were started but could not be increased due to degree of hypotension. This case highlights a rare manifestation of an exceedingly rare autoimmune condition associated with high mortality. Given the variability of cardiac involvement in the disorder, a high clinical suspicion is needed to establish an early diagnosis and pursue aggressive treatment with up-front combination immunomodulating therapy, which has been associated with improved outcomes.