Changes in the cytoskeletal proteins, sarcoplasmic reticulum, and capillaries in acute relaxant-steroid myopathy (ARSM) in contrast to the corticosteroid myopathy.

Since we reported a case of acute relaxant-steroid myopathy (ARSM) in 1994, we continued histological studies and compared the findings with those in a case of corticosteroid myopathy (CM). It was revealed that (1) dystrophin, spectrin, beta dystroglycan, and sarcoglycans on the cell surface were decreased, (2) regular arrangement of the sarcoplasmic reticulum was lost, and (3) some capillaries were degenerated. Since none of these changes were seen in CM, it became clear that ARSM is different from CM. It was estimated that continuous administration of non-depolarizing muscle relaxant produces a state akin to denervation. Combination of denervation, immobilization and circulatory disturbance in ARSM not only augments the effects of corticosteroids, but they produce changes different from CM, namely impairment of the cell membrane system (both internal and external) and capillary degeneration.