Typical muscle biopsy findings in inclusion body myositis

(A) Cross-sections of H&E-stained muscle biopsies demonstrate scattered inflammatory foci with lymphocytes invading or surrounding healthy-appearing muscle fibers combined with autophagic vacuoles with bluish-red material in areas not invaded by T cells and chronic myopathic features (increased connective tissue, atrophic and hypertrophic fibers). (B) In clinical inclusion body myositis, there is inflammation without vacuoles. (C) Characteristic in typical inclusion body myositis are COX-negative fibers and (D) crystal violet-positive congophilic amyloid deposits within the vacuoles. (Contributed by Dr. Marinos Dalakas.)