n patients with inclusion body myositis (IBM), selectivity of involvement of certain muscle groups is common, but the mechanism remains unclear. We report 2 patients with IBM showing selective distribution of weakness in limb muscles. The muscle biopsy revealed the typical features of IBM. Patient 1 underwent the second muscle biopsy because clear abnormality was not seen in the first biopsy specimen performed 15 years ago. Patient 2 was given a diagnosis after the first muscle biopsy. In cryostat sections of biopsy specimens from both patients, some fascicules showed prominent inflammatory features and others showed a normal appearance. In the present patients, the degree of inflammation was heterogeneous between individual muscles and individual fascicules in a muscle, resulting in the diagnostic difficulty.
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