More Than Muscle Aches: A Case of Statin-Associated Necrotizing Myositis

Statin-associated immune-mediated necrotizing myopathy (SINAM) is a rare but increasingly recognized autoimmune condition in which progressive proximal muscle weakness develops in statin-exposed patients and persists after drug discontinuation, driven by autoantibodies targeting HMG-CoA reductase. We report a 70-year-old woman who developed subacute progressive bilateral lower-extremity weakness on a background of nearly a year of asymptomatic, gradually worsening elevation of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), the standard liver enzymes, following more than three years of atorvastatin therapy. Diagnosis of anti-HMG-CoA reductase (anti-HMGCR) antibody-positive immune-mediated necrotizing myopathy (IMNM) was established by an isolated anti-HMGCR antibody level of 209 units (normal less than 20 units) in the setting of a uniformly negative standard myositis-specific antibody panel, confirming that anti-HMGCR must be requested as a separate assay. She was managed with atorvastatin discontinuation, high-dose corticosteroids, and escalation to intravenous immunoglobulin (IVIG) following biochemical relapse on steroid taper. This case highlights three teaching points: skeletal muscle as a frequently overlooked source of AST and ALT elevation in statin-treated patients, the necessity of dedicated anti-HMGCR testing when persistent post-statin myopathy is suspected, and the emerging serologic subtype-specific approach to second-line immunotherapy in IMNM.