Statin-Associated Anti-HMGCR Immune-Mediated Necrotizing Myopathy with Atypical Cutaneous Manifestations: Diagnostic Challenges - A Case Report

Introduction Immune-mediated necrotizing myopathy (IMNM) is a rare subtype of idiopathic inflammatory myopathy characterized by severe proximal muscle weakness, markedly elevated serum creatine kinase (CK), and myofiber necrosis with minimal inflammation. The anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibody associated form is frequently triggered by statin exposure but rarely presents with skin lesions. Case Presentation We present the case of a 77-year-old woman with a history of hypertension, dyslipidemia, and asthma on long term statin therapy who developed rapidly progressive proximal weakness following a viral upper respiratory tract infection. Neurological examination revealed symmetric proximal tetraparesis (BMRC 4/5 upper limbs, 2/5 lower limbs) and incomplete left ptosis. Skin examination showed erythematous, polymorphic lesions around the elbows and knees. Laboratory evaluation revealed severe hyperCKemia (12,316 U/L) and inflammatory markers elevation. Electromyography revealed a myopathic pattern with spontaneous activity, and muscle biopsy showed necrotic and regenerating fibers with minimal inflammatory infiltrate and diffuse MHC-I overexpression. Anti-HMGCR antibodies were positive, confirming the diagnosis of statin-induced anti-HMGCR IMNM. Treatment with high-dose corticosteroids led to marked clinical and biochemical improvement. Conclusion: This case highlights an uncommon presentation of anti-HMGCR IMNM with atypical cutaneous manifestations mimicking dermatomyositis. Recognition of such features may prevent diagnostic delay and guide appropriate immunosuppressive therapy.