What is sporadic inclusion body myositis (s-IBM)?

Updated: Jun 08, 2018
  • Author: Michael P Collins, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Sporadic inclusion body myositis (s-IBM) and hereditary inclusion body myopathies (h-IBM) encompass a group of disorders sharing the common pathological finding of vacuoles and filamentous inclusions. [1] They collectively demonstrate a wide variation in clinical expression, age of onset, associated diseases, and prognosis. This article focuses on s-IBM. For discussion of h-IBM, the reader is referred to other sources. [2, 3]

The term inclusion body myositis was originally used by Yunis and Samaha in 1971 for a case of myopathy that phenotypically suggested chronic polymyositis but showed cytoplasmic vacuoles and inclusions on muscle biopsy. In the subsequent years, s-IBM has been increasingly recognized and reported, primarily because of increased awareness of the condition and improved histologic techniques. A relatively common myopathic process, s-IBM is an important diagnostic consideration in the evaluation of progressive weakness in older Caucasian males.

Expression of s-IBM is variable, but all cases eventually evolve into a syndrome of diffuse, progressive, asymmetric, proximal, and distal weakness that is generally refractory to immunosuppressive treatment.

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