Inclusion-Body Myositis (IBM)

Causes/Inheritance

In most cases, the cause of inclusion body myositis (IBM) is unclear. Some viral infections or exposure to certain drugs have been reported to trigger IBM. In general, researchers believe that factors related to the immune system, genetics, aging and the environment all play a role in IBM development.

IBM is sometimes called sporadic IBM (sIBM) to indicate that it develops spontaneously and is not inherited. There are rare cases of two family members having IBM, which are referred to as familial IBM (fIBM). IBM does not typically run in families, however, and causative genetic mutations have not been found in most people with IBM.

IBM progression is known to involve two distinct processes, autoimmunity (a defect where the body’s immune system attacks its own tissues) and muscle degeneration. Many researchers now believe that autoimmunity may trigger IBM and result in the degenerative changes seen in muscles.

Specific changes have been shown to take place in the muscles of people with IBM. First, inflammatory immune cells invade the skeletal muscles and cause damage to the muscle tissues. The muscle cells also accumulate clumps of proteins (e.g. protein aggregates) from dead and damaged cells, which can be seen when the muscle tissue is viewed under a microscope. These clumps are the “inclusion bodies” for which the disease is named. The events that trigger these changes and the sequence of changes that leads to disease are not well understood.

References

1. Aljohani, N. I., Carette, S. & Lipton, J. H. Inclusion body myositis in a patient with chronic myeloid leukemia treated with dasatinib: A case report. J. Med. Case Rep. (2015). doi:10.1186/s13256-015-0674-9
2. Rodriguez-Pintó, I. & Shoenfeld, Y. Myositis and Vaccines. in Vaccines and Autoimmunity (2014). doi:10.1002/9781118663721.ch37
3. Valiyil, R. & Christopher-Stine, L. Drug-related myopathies of which the clinician should be aware. Current Rheumatology Reports (2010). doi:10.1007/s11926-010-0104-3
4. Ranque-Francois, B. et al. Familial inflammatory inclusion body myositis. Ann. Rheum. Dis. (2005). doi:10.1136/ard.2004.025494
5. Greenberg SA. Inclusion body myositis: clinical features and pathogenesis. Nat Rev Rheumatol. 2019;15(5):257-272. doi:10.1038/s41584-019-0186-x