Immune-Mediated Necrotizing Myopathy (IMNM)

Causes/Inheritance

In most cases, the cause of idiopathic inflammatory myopathies (IIM), the disease group that encompasses immune-mediated necrotizing myopathy (IMNM), is unclear. For some reason, the body’s immune system turns against its own tissues in an autoimmune process. In IMNM, this autoimmune process leads to the necrosis (death) of muscle fibers. This necrosis can be reversible if treatment is started early.

IMNM is not a genetic disorder, although there may be genetic factors that make it more or less likely that an IIM will develop. A combination of genetic, immune, and environmental factors is thought to contribute to development of the IIMs. Some environmental triggers that have been associated with IIMs include viral infection and certain medications. In the case of anti-HMGCR IMNM, exposure to statins has been highly associated with the development of disease.

References

1. Dalakas MC. Inflammatory Muscle Diseases. Longo DL, ed. N Engl J Med. 2015;372(18):1734-1747. doi:10.1056/NEJMra1402225
2. Pinal-Fernandez I, Casal-Dominguez M, Mammen AL. Immune-Mediated Necrotizing Myopathy. Curr Rheumatol Rep. 2018;20(4):21. doi:10.1007/s11926-018-0732-6
3. Allenbach Y, Mammen AL, Benveniste O, Stenzel W, Immune-Mediated Necrotizing Myopathies Working Group. 224th ENMC International Workshop:: Clinico-sero-pathological classification of immune-mediated necrotizing myopathies Zandvoort, The Netherlands, 14-16 October 2016. Neuromuscul. Disord. NMD 2018;28:87–99.

Last update: Feb 2023
Reviewed by Julie Paik, MD, MHS; Johns Hopkins University