Inclusion body myositis: Update

Purpose of review: To examine new developments in sporadic inclusion body myositis (IBM), including updated clinical and prognostic factors, novel autoantibody associations, unique histopathologic findings, proposed new clinical diagnostic criteria, and novel therapeutic agents. Recent findings: IBM is a slowly progressive disease, leading to wheelchair use, on average, 12-20 years after onset of symptoms; however, it does not appear to interfere with life expectancy. Older age at the onset of first symptoms as well as immunosuppressive therapy are likely associated with more rapid disease progression. Quantitative muscle strength of knee extensor and the IBM functional rating scale seem to be sensitive disease progression markers and may be useful clinical trial outcome measures. Newly proposed diagnostic criteria utilize data-driven approaches with very high sensitivity and specificity. A novel autoantibody, as well as unique proteins seen histopathlogically, may help hone in on diagnosis as well as to deepen our understanding of IBM pathophysiology. Novel treatments, including follistatin and bimagrumab, are directed at potential therapeutic targets. Summary: We have observed an explosion of knowledge in IBM in the recent past, which challenges traditional dogma and ushers in a new era of understanding with potential clinical implications for those who suffer with IBM.