Clinical failure of botulism toxin A in movement disorders

OBJECTIVE: Botulinum toxin (BTX) injections have been used extensively in medicine; however, little is known about the factors predicting the loss of effectiveness of botulin toxin. METHODS: Using a clinical database, we identified 401 subjects who had been treated for movement disorders from 1998 through 2010 with onabotulinumtoxin A (BTX A) or who switched from BTX A to rimabotulinumtoxin B (BTX B). We compared patients who switched from type A to type B with patients using type A only with regard to number of visits, total number of injections, number of initial and final sites, number of initial units used, and duration of treatments. RESULTS: We observed that patients who switched from BTX A to B had a significantly higher number of initial injection sites than patients with BTX A only (BTX A to B median = 8.5; BTX A median = 6; p for difference = 0.006), had a higher number of final sites (BTX A to B median = 9 BTX A median = 7; p = 0.01), and were also more likely to have multiple reasons for injection (BTX A to B = 25.0%; botulin toxin A = 5.3%; p = 0.01). We did not find significant differences between groups based on the other variables. CONCLUSIONS: Our findings suggest that higher number of sites rather than higher number of units or years of treatment are associated with the loss of effectiveness to BTX A. It is possible that the loss of effectiveness to the BTX is more strongly elicited when the injections are widely diffuse.