The muscle biopsy is required for a definite diagnosis. The cause of IBM is unknown. About 1 in 10 cases may be hereditary, however these cases are clinically and pathologically distinct. All of these, and more, are only proposed mechanisms. The cause is still uncertain.
Physical therapy can be helpful in maintaining mobility.
The prognosis is a slow progressive disease with little chance of remission. Most patients remain ambulatory although often need some assistance.