Necrotizing myopathies: an update.

Necrotizing myopathy is defined by the predominant pathological feature of necrosis of muscle fibers in the absence of substantial lymphocytic inflammatory infiltrates. Most commonly necrotizing myopathies are divided into immune mediated (IMNM) and nonimmune mediated (NIMNM). IMNM has been associated with anti-signal recognition particle antibodies, connective tissue diseases, cancer, post-statin exposure with 3-hydroxy-3-methylglutaryl-coenzyme A antibodies, and viral infections including HIV and hepatitis C. NIMNM is linked to medications and toxic exposures. Both IMNM and NIMNM are typically characterized by proximal weakness, although the severity can vary substantially. Myalgias are reported by some, but not all, patients. Pathological findings on muscle biopsy include predominant fiber necrosis with little or no inflammatory infiltrate. In IMNM, there is variable evidence for the deposition of membrane attack complex on capillaries and muscle fibers, although membrane attack complex deposition on capillaries is typically less than is seen in dermatomyositis; class I major histocompatibility complex expression on muscle fibers is variable but typically less than is seen in polymyositis. Immunohistochemical abnormalities are not typically seen in NIMNM. Treatment of IMNM involves immunosuppressive therapy, although there are no controlled trials to guide particular treatment choices. Treatment of NIMNM involves removal of the toxic exposure.