A Rare Case of Anti-HMGCR-Positive Immune-Mediated Necrotizing Myopathy Associated With Statin Use

Statin-induced necrotizing autoimmune myopathy (SINAM) is a rare complication of chronic statin use that occurs in individuals aged 50 years and older, with statin exposure ranging from two months to 10 years. While common side effects of statins, such as self-limited myalgia and elevated creatine kinase (CK) levels or rhabdomyolysis, usually resolve with discontinuation, SINAM presents with more severe, persistent, and debilitating symptoms. We describe the case of an elderly man with no prior history of muscle weakness or statin-associated myopathy who presented with dysphagia and progressive weakness in both upper and lower extremities. He was initially diagnosed with statin-induced rhabdomyolysis and received supportive care. However, due to a lack of clinical improvement and based on an expanded literature review, SINAM was suspected. Empiric steroid therapy was initiated, and subsequent anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibody testing returned positive, confirming the diagnosis. This case provides evidence on the use of steroid monotherapy in achieving disease remission. Additionally, it underscores the critical importance of maintaining a high index of suspicion and utilizing evidence-based approaches, especially when common investigative techniques yield no definitive cause. Early recognition and treatment of SINAM are essential to improve patient outcomes.