No Muscle Left Behind: Cardiac Arrest and Myocarditis in a Patient With Idiopathic Inflammatory Myopathy

Idiopathic inflammatory myopathies (IIM) are known to have extramuscular involvement, the most concerning of which is the involvement of the myocardium. Constituting a large burden of morbidity and mortality, there remains a paucity of literature describing cardiac manifestations in inflammatory myopathies, and definitive treatment and screening guidelines have yet to be published. Here, we present a rare case of cardiac arrest and fulminant myocarditis in a patient with newly diagnosed myositis. A 71-year-old non-Hispanic White male with type 1 diabetes mellitus and hyperlipidemia presented to the rheumatology clinic with five months of progressive proximal muscle weakness and myalgias accompanied by a persistently elevated creatine kinase level and elevated liver-associated enzymes despite cessation of atorvastatin therapy three months prior. The initial examination was notable for reduced quadriceps strength bilaterally and the absence of visible skin rashes. He was found to have positive anti-Mi-2 antibody, elevated aldolase, and positive antinuclear antibody in a speckled pattern. After magnetic resonance imaging (MRI) of the left thigh demonstrated a pattern consistent with inflammatory myositis, steroid therapy was initiated, and he was referred for muscle biopsy to confirm the presumptive diagnosis of dermatomyositis. Two weeks later, before a muscle biopsy could be performed, the patient experienced a witnessed pulseless electrical activity (PEA) cardiac arrest from which he was successfully resuscitated by emergency medical services prior to hospital arrival. Subsequent cardiac evaluation showed a nonischemic cardiomyopathy with evidence of myocarditis on cardiac magnetic resonance (CMR) imaging with inferior wall hypokinesis and a left ventricular ejection fraction (LVEF) of 27%. He underwent placement of a subcutaneous implantable cardioverter defibrillator (ICD), and he responded well to intravenous immunoglobulin (IVIG), diuresis, and initiation of guideline-directed medical therapy with post-treatment transthoracic echocardiogram (TTE) demonstrating an LVEF of 40%. This case highlights one of the rather protean and severe cardiac manifestations of IIM. Typically, the cardiac manifestations observed in IIM include subclinical electrocardiogram (ECG) and echocardiographic changes but can present, as detailed here, with fulminant myocarditis and heart failure (HF). Our purpose herein is to heighten clinician awareness of and advocate for the establishment of definitive screening and management guidelines for cardiac disease in idiopathic inflammatory myopathies.