Autoimmune myopathy

**Definition:** Autoimmune myopathy is a 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. It is often accompanied by statin therapy, connective tissue diseases, cancer, and autoantibodies specific for signal recognition particle (SRP) or 3-hydroxy-3-methylglutaryl–coenzyme A reductase (HMGCR).

**Exclusions:** - Myasthenia gravis or certain specified neuromuscular junction disorders - Primary disorders of muscles