Inclusion body myositis with Sjögren disease and M-proteinemia: a case report and literature review

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We report a case of inclusion body myositis complicated by Sjögren disease (SjD) and M-proteinemia, in which glucocorticoid (GC) administration resulted in M-protein disappearance and improved muscle strength. A 62-year-old woman presented with a 5-year history of dry mouth and eyes, and a 3-month history of bilateral lower limb muscle weakness as her chief complaint. Weakness was noted in the iliopsoas and deep finger flexor muscles. A muscle biopsy led to a diagnosis of inclusion body myositis, with concomitant SjD and M-proteinemia. Following GC administration, the M-protein disappeared and muscle strength improved. The M-protein in this case was considered benign M-proteinemia caused by an excessive immune response. This case suggests that immunotherapy may be effective in inclusion body myositis, which has a strong immune-mediated component.