[Acquired necrotizing myopathies]

Necrotizing myopathies (MN) are defined by a specific histological pattern. They are characterized by a predominant muscle fibre necrosis and regeneration but with little or no associated inflammation. This histological pattern is observed in acquired myopathy but also in muscular dystrophy. Acquired NM can be secondary to drugs or toxics, and if not, autoimmune mechanisms have to be suspected. Necrotizing autoimmune myopathy is recognized as a subgroup of idiopathic inflammatory myopathies, different from other myositides. Generally, patients present a rapidly progressive and severe symmetrical proximal weakness with high serum creatine kinase level, associated in some patients with cardiac involvement. On the other hand, a slower progression may sometimes be observed, that could lead to erroneous diagnosis of muscular dystrophy. Necrotizing autoimmune myopathy may be associated to specific autoantibodies against signal recognition particle, or more recently described, against 3-hydroxy-3-methylglutaryl-coenzyme A reductase. Necrotizing auto-immune myopathy can also be described in association with connective tissue diseases such as lupus or sclerodermia. In remaining cases, cancer association may be observed. Necrotizing autoimmune myopathies are now considered as a new entity, treatable by immunosuppressants and which should not be misdiagnosed as a muscular dystrophy.