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74-year-old man with a 4-year history of asymmetric lower limb muscle weakness.
Inclusion body myositis (IBM) is an idiopathic progressive myopathy with inflammatory and degenerative features. Affected patients are generally >50 years of age with a pattern of proximal and distal weakness that is asymmetric involving both the upper and lower extremities. The natural history is insidious and progressive, and does not respond to steroid therapy. Microscopically, muscle biopsy generally shows atrophic and hypertrophic fibers, necrotic and regenerating fibres, endomysial fibrosis, a T-cell predominant endomysial inflammatory infiltrate, and characteristic rimmed vacuoles within muscle fibres. The rimmed vacuoles contain aggregate-prone proteins typically seen in neurodegenerative diseases such as beta-amyloid, tau, and TDP-43 (see Related Content) as well as autophagic markers such as ubiquitin and p62. The pathogenesis of and relationship between the inflammatory and degenerative (protein aggregate) components of IBM are the major foci of current research.
See Related Content for references:
1) Weihl, CC et al. Neuropath Appl Neuro 2017 Jan 23