MUSCLE-FIBER ATROPHY IN LEG MUSCLES AFTER BOTULINUM TOXIN TYPE-A TREATMENT OF CERVICAL DYSTONIA

Previous electrophysiologic studies on the effects of local injections of botulinum toxin type A (BTX-A) have indicated impaired neuromuscul ar transmission in distant muscles. To further study possible distant effects of repeated BTX-A injections, we obtained percutaneous muscle biopsies of the vastus lateralis muscle from 11 patients with cervical dystonia. We examined the biopsies with histopathology and morphometr y, and compared them with age-matched healthy controls. There was an i ncreased frequency of angular atrophic type IIB fibers in the patient group, and the mean size of IIB fibers was significantly smaller (p <0 .05). In addition, there was a negative correlation between accumulate d dose of botulinum toxin and relative size of type IIA fibers (p <0.0 5). We postulate that the observed atrophy is due to distant effects o f botulinum toxin causing progressive denervation-like changes in non- treated muscle. This observation calls for further, prospective studie s of the long-term effects of the treatment.