Statin-Associated Necrotizing Autoimmune Myopathy: Unmasking 3-Hydroxy-3-Methylglutaryl-CoA Reductase (HMGCR) Antibody-Positive Disease After Statin Re-exposure.

Necrotizing autoimmune myopathy (NAM) is an uncommon inflammatory muscle disease marked by progressive weakness and elevated muscle enzymes. In some individuals, it may develop in association with statin use, particularly when specific autoantibodies are present. We report the case of a 65-year-old man who experienced worsening, painless proximal muscle weakness and significant creatine kinase (CK) elevation shortly after resuming statin therapy following a temporary discontinuation. The absence of myalgias or systemic symptoms obscured the diagnosis, and initial elevations in liver enzymes were misattributed to known hepatic steatosis during outpatient evaluation. Diagnostic workup revealed positive 3-hydroxy-3-methylglutaryl-CoA reductase antibodies (HMGCR Ab), magnetic resonance imaging (MRI) findings consistent with inflammatory myopathy, and a muscle biopsy demonstrating scattered necrotic and regenerating fibers, characteristic of immune-mediated necrotizing myopathy (IMNM). This case highlights the potential for statin re-exposure to unmask or exacerbate evolving NAM in patients with subclinical disease. Clinicians should maintain a high index of suspicion for NAM in statin-treated individuals presenting with unexplained muscle weakness or transaminitis. Early recognition and timely initiation of therapy are critical to prevent irreversible muscle damage and improve clinical outcomes.