IBM is classified as an inflammatory myopathy, indicating the presence of immune system cells within muscle tissue.
The name itself, inclusion body myositis, is derived from the clumps of discarded cellular material—the "bodies"—that collect within muscle tissue. Myopathy is a muscle disease and inflammation is the body’s response to cell damage. Another term used to refer to inflammatory myopathy is myositis, “myo” meaning muscle, and “itis” meaning inflammation.
Inflammatory cells invading muscle tissues is characteristic of IBM, but the disease is distinct from other inflammatory myopathies in that muscle degeneration also occurs.