A new target for the treatment of trigeminal neuralgia with botulinum toxin type A.

Trigeminal neuralgia (TN) is typically treated pharmacologically with anticonvulsants, but these can be ineffective, or can lose their effectiveness over time. In recent years, botulinum toxin type A (BoNT-A), when injected subcutaneously across multiple sites, can effectively treat TN. However, approximately 30% of TN cases are refractory to subcutaneous BoNT-A treatment. We report here the case of a 79-year-old female patient with TN presenting as severe, episodic pain in the lower left gingival area. She was on anticonvulsant therapy (carbamazepine) for about 3 years prior to BoNT-A treatment. Despite initial relief, the pain not only recurred, but also began to worsen, even as her carbamazepine dose was increased substantially. We injected 50 U of BoNT-A into the oral mucosa of the painful gingival area, but the patient's pain was unaffected. We then changed to an intramuscular injection protocol and injected the same dose of BoNT-A into the left masseter, which produced a good therapeutic effect for about 5 months; she was then administered a second treatment (intra-masseter), and at a 2-week follow-up, still reported being pain-free. This case and a survey of the literature suggest that BoNT-A injection protocols maybe closely correlated with their clinical efficacy in cases of TN, possibly due to the ability of BoNT-A to be transported retrogradely along trigeminal nerve axons. We believe that finding the optimal BoNT-A therapy injection protocol(s) will significantly reduce the number of refractory cases of TN.