Alleviation of pain and reduction of muscle hypertension by botulinum toxin A

Botulinum toxin A (BoNT-A) develops its muscle-relaxing effect by the inhib ition of acetylcholine (ACh) release. This toxin is also known to relieve m uscular pain in different disorders. Conspicuously, pain in some patients r esponds earlier and sometimes even better than muscle tension, indicating t hat the effect of BoNT-A on pain is not only due to inhibition of ACh relea se. A questionnaire was distributed to 88 patients suffering from cervical dystonia (CD). Thirty-five completed questionnaires could be used for data analysis. After intramuscular injections of BoNT-A, patients with CD experi ence significant reductions in pain which sometimes occur significantly ear lier than the improvements in head posture. In the iris sphincter muscle of the rabbit and in dorsal root ganglion cells (DRG) of the rat, inhibition of the release of substance P by BoNT-A has been shown experimentally,and B oNT-C has been proven to develop endopeptidase activity toward substance P (SP) in vitro. Findings in the current literature and our observations allo w the conclusion that alleviation of muscle pain by BoNT-A may also be due to an effect on the release of nociceptive neuropeptides, among which SP se ems to have a key function.