Effect of muscle activity and botulinum toxin dilution volume on muscle paralysis

The purpose of this study was to evaluate the effects of botulinum toxin A (BTX‐A, Botox) dilution volume and post‐injection exercise with electrical stimulation on muscle paralysis. We injected 10 units of BTX‐A diluted with 0.1 ml (B1, n=8) or 0.5 ml (B5, n=8) normal saline into both gastrocnemius muscles of 16 New Zealand white rabbits; two controls received no BTX‐A. After BTX‐A injection, all rabbits received calf muscle stretching exercise and electrical stimulation for 2 hours on the left leg. The compound muscle action potential (CMAP) decrease was most pronounced at 1 week and progressive recovery was observed (i.e. recovery from paralysis, increase of CMAP). There was a significant decrease of CMAP amplitudes in the B5 group compared with the B1 group at week 1 and week 4 (p<0.001). Left limbs with stretching exercise and electrical stimulation showed lower CMAP amplitudes compared with control right limbs of all rabbits. To maximize the muscle paralysis effect of BTX‐A, increasing dilution volume and performing post‐injection stretching exercise with electrical stimulation may be a promising strategy for increasing the beneficial effect of BTX‐A treatment. Future studies are needed to investigate the clinical application of this finding.