Chronic Anti-HMG-CoA Reductase Positive Necrotizing Myositis With Remote Exposure to Statins

The use of statins may be associated with muscle-related side effects ranging from myalgia to rhabdomyolysis. A rare adverse effect is statin-induced anti-hydroxy-3-methyl-glutaryl-coenzyme A reductase (anti-HMGCR) necrotizing myositis, which may develop after exposure to statins due to autoantibodies against HMG-Co-A reductase. We present the case of a 76-year-old male who developed progressive muscle weakness three years after exposure to statins. He had significantly elevated creatine kinase (CK) levels, despite the discontinuation of statins three years prior. He complained of generalized muscle weakness, and examination revealed reduced strength, especially in the proximal musculature. MRI revealed inflammatory myositis of the medial and posterior compartments of bilateral thighs. Autoimmune workup was positive for anti-HMG-CoA reductase antibodies. Muscle biopsy showed endomysial inflammation with fibrosis and fat replacement, suggesting chronic but active myositis. A diagnosis of chronic anti-HMGCR necrotizing myositis was made. The patient was started on oral prednisone and methotrexate with improvement in symptoms and CK levels. This case highlights a chronic form of a rare cause of myositis that may be a challenge to diagnose given the remote exposure to statins.