|The first muscles affected in inclusion-body myositis are usually those of the wrists and fingers, and the muscles at the front of the thigh. The muscles that lift the front of the foot also may be affected.|
IBM is one of the inflammatory myopathies, a group of muscle diseases that involves inflammation of the muscles or associated tissues, such as the blood vessels that supply the muscles. A myopathy is a muscle disease, and inflammation is response to cell damage.
Another word for inflammatory myopathy is myositis. The myo root means muscle, and the itis root means inflammation; so a myositis is an inflammatory muscle disease.
Inflammatory cells invading muscle tissues is one characteristic of IBM, but the disease is distinct from other inflammatory myopathies in that muscle degeneration also occurs. IBM is named for the clumps of discarded cellular material — the "bodies" — that collect in the muscle tissues.
There are some genetic forms of IBM in which, for the most part, inflammation isn’t a major part of the picture. For this reason, these forms are often called inclusion-body myopathy (muscle disorder), leaving out the “itis” in the disease name to reflect the relative lack of inflammation. For more, see Causes/Inheritance.
IBM causes progressive weakness of the muscles of the wrists and fingers, the muscles of the front of the thigh, and the muscles that lift the front of the foot. Unlike in other inflammatory myopathies, the heart and lungs are not affected in IBM. For more, see Signs and Symptoms.
The cause of inflammatory myopathies like IBM is unclear. For some reason, the body’s immune system turns against its own muscles and damages muscle tissue in an autoimmune process. The cause of the muscle degeneration that occurs in IBM is unclear as well.
Genetic forms of IBM can be either dominant or recessive. For more, see Causes/Inheritance.
IBM is primarily a disease of men, but women also can be affected. Its onset is typically after age 50 and progression is slow. Currently there are no medications to treat IBM, but the disease isn't considered life-threatening. Most people with IBM remain able to walk, although they may require a cane or wheelchair for long distances.
New research is rapidly leading to increased understanding of IBM. Scientists are examining factors that may trigger the disease such as viruses, certain drugs or vaccines. All these factors are being studied so inflammatory myopathies like IBM can someday be better understood, treated or perhaps prevented entirely.