Anti-HMGCR (Hydroxy-3-Methylglutaryl-CoA Reductase) Myopathy: A Rare Cause of Proximal Muscle Weakness

Idiopathic inflammatory myopathy (IIM) represents a rare group of autoimmune conditions resulting in muscle weakness and includes polymyositis, dermatomyositis, immune-mediated necrotizing myopathy (IMNM), overlap myositis, and inclusion body myositis. Anti-3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) antibody IMNM represents a rare but increasingly recognized subtype of IIM. Here we report a case of a 65-year-old woman on rosuvastatin who presented with two months of progressive proximal muscle weakness, significant truncal weakness, and elevated creatine kinase concerning for rhabdomyolysis and inflammatory myopathy. The patient was eventually diagnosed on day 8 of her hospital stay with anti-HMGCR antibody IMNM after delayed testing for this specific myopathy. Increased awareness of this IIM subtype, as well as its risk factors and presenting features, might improve rapidity of testing and shorten hospital stays if the diagnosis is considered in the emergency department or early in the hospital course.