3-Hydroxy-3-Methylglutaryl-Coenzyme A Reductase Antibody-Positive Immune-Mediated Necrotizing Myopathy With Transaminitis and Nonspecific Liver Biopsy Findings in a Statin-Naive Patient

Anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (anti-HMGCR) immune-mediated necrotizing myopathy (IMNM) causes proximal weakness and marked creatine kinase (CK) elevation.Serum aminotransferases may also increase with muscle injury and be mistaken for primary liver disease.We describe a 64-year-old man without statin exposure who developed five months of progressive proximal weakness and weight loss.CK and aminotransferases were markedly elevated, and anti-HMGCR antibodies were strongly positive.Hepatitis and autoimmune liver testing were unrevealing; liver biopsy showed mild nonspecific changes.Pulse methylprednisolone, intravenous immunoglobulin (IVIG), and a prednisone taper produced early functional improvement.Alanine aminotransferase (ALT) normalized by approximately 6 months and aspartate aminotransferase (AST) by approximately 13 months, whereas CK first returned to its reference interval at approximately 18 months and remained normal at approximately 21 months.The clinical phenotype, severe hyperCKemia, anti-HMGCR seropositivity, magnetic resonance imaging findings, and longitudinal biochemical response favored a major skeletal muscle contribution to the aminotransferase elevation, although a concurrent mild hepatic process could not be definitively excluded; the biopsy did not demonstrate anti-HMGCR-mediated hepatic injury.Early CK measurement in patients with proximal weakness and transaminitis can clarify the source, while liver evaluation remains appropriate when supported by cholestatic markers, synthetic dysfunction, imaging, or histology.