This study proposes to accomplish these goals through an exploratory comparison of the clinical efficacy and natural history of BTX measured at weekly time intervals. Subjects reporting short (<10 weeks) duration of benefit and subjects reporting long (>10 weeks) duration of clinical benefit will provide the primary comparison. Histological examinations (in a subset of subjects) of neuronal changes associated with regeneration of terminal neuronal endplates will be used to support these clinical observations. This study will follow subjects through 3 injection cycles or 36 weeks. Biopsies will be performed on consenting subjects prior to their first and second injection cycles.