Light and electron microscopic (EM) features of sporadic inclusion body myositis vacuolated muscle fibers. Engel trichrome staining demonstrating typical vacuolated muscle fibers (A–D). On a given 10 µm transverse section, vacuoles are of various sizes; some contain floccular pinkish material, and some appear empty. Only one vacuole, in (C), appears to have a slight rim. (E) Transmission EM shows a vacuole containing inclusions consisting of numerous, various‐sized membranous whorls of autophagosomal/lysosomal debris. A–D, *2100; E, ×50 000.