A case of asymptomatic hyperCKemia for 40 years leading to a diagnosis of treatable immune-mediated necrotizing myopathy

Immune-mediated necrotizing myopathy (IMNM) is a rare but treatable inflammatory myopathy characterized by severe muscle necrosis with minimal inflammatory infiltration. IMNM typically presents with progressive proximal muscle weakness and markedly elevated serum creatine kinase (CK) levels. Here, we report a unique case of IMNM associated with anti-signal recognition particle (SRP) antibody, in which hyperCKemia persisted for 40 years before the onset of muscle symptoms. The extremely prolonged asymptomatic course initially suggested a hereditary myopathy; however, the absence of selective fatty replacement on muscle MRI pointed toward an inflammatory etiology. This imaging finding guided the diagnosis toward IMNM, a treatable condition, and led to successful immunotherapy with normalization of CK levels and marked improvement in muscle strength over 12 months.