Necrotizing autoimmune myopathy

PURPOSE OF REVIEW: Necrotizing autoimmune myopathy (NAM) is a relatively newly recognized subgroup of idiopathic inflammatory myopathies, which despite diverse causes, have the common histopathological features of myocyte necrosis without significant inflammation. Patients present with a subacute severe symmetrical proximal myopathy, associated with a markedly elevated creatine kinase level. These are most likely immune-mediated, as they respond to immunotherapy. The review aims to define this heterogeneous entity and summarize the salient clinical, laboratory, and muscle biopsy findings, in order to facilitate the diagnosis and treatment of this condition. RECENT FINDINGS: Statin-associated NAM has been linked with an antibody against the 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) protein, which is up-regulated in regenerating fibres. This finding suggests that NAM is an antibody-mediated disease, and may explain the continuing progression of disease despite cessation of the statin. In addition it may provide a useful diagnostic test in the future, to help differentiate immune from nonimmune statin myopathies. SUMMARY: It is important to recognize and distinguish NAM from other causes of myocyte necrosis, because it has the potential of being amenable to treatment.