SPORADIC INCLUSION-BODY MYOSITIS - COUNTS OF DIFFERENT TYPES OF ABNORMAL FIBERS

Invasion of nonnecrotic muscle fibers by cytotoxic T cells, accumulati on of congophilic amyloid inclusions in muscle fibers, and fiber necro sis are consistent histologic findings in sporadic inclusion body myos itis (IBM). To evaluate the relative significance of these alterations , we quantitatively analyzed the frequency of these abnormalities in 3 1 electron microscopy proven cases of IBM (20 untreated and 11 immunos uppressed). Nonnecrotic muscle fibers invaded by T cells were severalf old more frequent than fibers displaying the other pathologic alterati ons. Comparison of muscle samples from treated and untreated patients revealed no significant differences in the respective frequencies of t he three species of abnormal fibers. Moreover, there was no correlatio n of the frequency of any abnormality either with disease duration or length of treatment. The much higher frequency of the invaded than Con go red-positive fibers points to the importance of an immune-mediated mechanism in the disease; but the basic cause of the disease remains u ndefined.