BackgroundStatins are one of the most frequently used drug groups among patients with cardiovascular disease. Muscle pain is very frequent among patients using statins. It is important to distinguish patients with benign muscle pain without significant biochemical correlates from patients with serious myopathies.Case summaryWe present the case of a 68-year-old woman taking atorvastatin in the past 8 months after a coronary bypass grafting, presenting with proximal muscle weakness and pain. Biochemical analysis showed a markedly elevated creatine kinase (CK) (24,159 U/L). Despite discontinuation of the statin and therapy for rhabdomyolysis (IV fluid, mannitol, and sodium bicarbonate), CK levels did not drop as much as expected. Muscle biopsy showed mild inflammatory changes and few necrotic muscle fibres, suggestive for an immune-mediated necrotizing myopathy (IMNM). Serology showed a high anti-HMG-CoA reductase antibody (anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase antibody) titre, diagnostic for an IMNM induced by statins. The patient was treated with corticosteroids and methotrexate. Creatine kinase levels, muscle weakness, and pain gradually improved over the following months.DiscussionIMNM induced by statins is a relatively new entity. It is important to be recognized because it is not a self-limiting adverse effect such as the frequent benign muscle pains caused by statins. Beside discontinuation of the causative statin, aggressive immunosuppressive therapy is mandatory in IMNM. Therefore, it is important to test for anti-HMGCR antibodies and if necessary perform a muscle biopsy in patients taking statins, presenting with muscle weakness, and CK elevations not improving after discontinuation of the statin.