ABSTRACT
The term inclusion body myositis (IBM) was introduced three decades ago to describe an adult-onset, acquired (sporadic) inflammatory myopathy with two unique histological features:1 cytoplasmic ‘rimmed’ vacuoles containing whorls of cytomembranes, and typical cytoplasmic and nuclear inclusions. Electron microscopy (EM) shows that these inclusions are composed of clusters of tubular filaments with a diameter of 14-18 nm. The vacuoles are not membrane bound, for the term rimmed refers to the extra basophilic stain around many of these vacuoles on hematoxylin and eosin staining. During the same period, a group of hereditary myopathies, each with its unique clinical features and ethnic cluster, was described. The histological and ultrastructural picture in these diverse myopathies is very reminiscent of sporadic IBM, with one clear exception: the absence of inflammation.1 This heterogeneous group is now called hereditary inclusion body myopathy (HIBM).
