Acquired necrotizing myopathies

Purpose of reviewNecrotizing myopathy exhibits a specific histological pattern, characterized by significant necrosis, with simultaneous muscle fiber regeneration, but without or with little inflammation. This histological pattern may be observed in acquired myopathies but also in muscular dystrophy. Acquired necrotizing myopathy can be secondary to drugs or toxics agents, and if not, autoimmune mechanisms have to be suspected. Necrotizing autoimmune myopathy (NAM) is now recognized as a subgroup of idiopathic inflammatory myopathies. This review aims to further describe the different acquired myopathies, with special focus on NAM since specific autoantibodies have been discovered.Recent findingsUsually, acquired myopathy has an acute onset, but a slower progression may sometimes be observed that could lead to erroneous diagnosis of muscular dystrophy. NAM may be associated with specific autoantibodies against signal recognition particle, or, as more recently described, against 3-hydroxy-3-methylglutaryl-coenzyme A reductase, especially in statin-exposed patients. Their presence permits affirmation that muscular necrosis is immune-mediated. The antibody titer is correlated to the disease activity.SummaryNAMs are now considered as a new entity, treatable by immunosuppressants, and should not be misdiagnosed as a muscular dystrophy.