RIMMED BASOPHILIC VACUOLES AND FILAMENTOUS INCLUSIONS IN NEUROMUSCULAR DISORDERS

To study the incidence of rimmed basophilic vacuoles (RBV) and 15-21 n m filamentous inclusions in neuromuscular disorders, other than inclus ion body myositis (IBM) and to determine the diagnostic value of RBV q uantitation in the differential diagnosis of IBM, we reviewed 1600 mus cle biopsies for RBV and 750 biopsies for filamentous inclusions. The number of RBV-positive fibers per 10 mm(2) - the RBV-fiber density - w as determined. The incidence of RBV in non-IBM biopsies was 8.8 per 10 00. Major diagnostic categories were neurogenic disorders (n = 7) and limb girdle muscular dystrophies (LGMD) (n = 3). In IBM (n = 7) the RB V-fiber density ranged from 10.4 to 63.1 and was significantly higher than in neurogenic disorders (0.9 - 4.4) and LGMD (1.1 - 2.7). The hig hest value was found in rigid spine syndrome (205.8). Filamentous incl usions were seen in 2.7 per 1000 non-IBM biopsies, including familial oculopharyngeal muscular dystrophy with distal myopathy (OPMD-DM), rig id spine syndrome, acid maltase deficiency and amyloid neuropathy. RBV and filamentous inclusions coexisted in rigid spine syndrome and in f amilial OPMD-DM. RBV, as well as filamentous inclusions, has a very lo w incidence in non-IBM neuromuscular disorders; the RBV-fiber density may help to discriminate neurogenic disorders and LGMD from