[A case of inclusion body myositis (IBM) associated with lipid-storage vacuoles]

A 62-year-old woman, who has had slowly progressive muscle weakness and wasting of the four limbs for past 10 years, was evaluated by muscle biopsies; i.e. the deltoid, a moderately atrophic muscle, and the quadriceps femoris, a muscle that was only mildly involved. The specimen from the deltoid disclosed the basic muscle structures having been collapsed, containing many fibers undergoing degeneration. There were rimmed vacuoles and infiltration of macrophages and round cells into the muscle fibers and perimysial space. Inclusion bodies containing fibrillary structures were identified in sarcolemmal nuclei by electron microscopy. When the quadriceps femoris muscle was examined, however, a large number of vacuoles were interspersed between myofibrils that contained numerous lipid droplets. There were no pathological changes suggestive of IBM in this specimen. The case described here is unique in that the muscle biopsies from two separate muscle revealed a distinctly different pathology. Although we were unable to determine the cause of lipid-storage in this case, it is our impression that inclusion body myositis is not a uniform disorder but the characteristic pathology to this particular myositis might be an ultimate feature of several diverse degenerative and/or inflammatory muscle disorders.