Light Chain Cardiac Amyloidosis With Skeletal Muscle Weakness.

BACKGROUND: Amyloid light chain (AL) amyloidosis can manifest with heterogeneous, multisystem features. Cardiac involvement is common and drives prognosis. CASE SUMMARY: A 54-year-old man presented with proximal muscle weakness, autonomic and gastrointestinal symptoms, and exertional intolerance. Skeletal muscle imaging suggested myositis. Cardiac evaluation revealed conduction disease, and echocardiography was consistent with infiltrative cardiomyopathy. Fluorodeoxyglucose positron emission tomography demonstrated myocardial uptake. Targeted biopsies confirmed AL amyloidosis. Plasma cell-directed therapy achieved a partial hematologic response. Given the t(11;14), the patient began a trial of a novel BCL-2 inhibitor. DISCUSSION: Fluorodeoxyglucose-avid myocardium is described in amyloidosis but is not diagnostic. When a concurrent plasma cell clone or other red flags are present, a high index of suspicion should be maintained for AL amyloidosis. TAKE-HOME MESSAGES: A high index of suspicion should be maintained for cardiac AL amyloidosis in patients with atypical cardiac findings. Unexplained muscle weakness should prompt evaluation for systemic AL amyloidosis even with subtle cardiac findings.