Botulinum Toxin-A, Generating a Hypothesis for Orofacial Pain Therapy

Orofacial pain encompasses a spectrum of disorders ranging from musculoskeletal disorders, such as myofascial pain, and temporomandibular disorders to neuropathic situations, such as trigeminal neuralgia and painful post-traumatic trigeminal neuropathy, and neurovascular pain such as orofacial migraine and cluster orofacial pain. Each require tailored prophylactic pharmacotherapy, such as carbamazepine, gabapentin, pregabalin, amitriptyline, metoprolol, and topiramate. Yet a substantial subset of patients remains refractory. Botulinum toxin type A (BoNT-A) has demonstrated growing efficacy in the treatment of multiple forms of orofacial pain, which covers the whole range of these disorders. We describe the analgesic properties of BoNT-A for each of the three following orofacial pain disorders: neuropathic, myofascial, and neurovascular. Then, we conclude with a section on the neuromodulatory mechanisms of BoNT-A. This lays the basis for the generation of a hypothesis for the segmental therapeutic action of BoNT-A on the whole range of orofacial pain disorders. In addition, the advantage of BoNT-A for providing a safe sustained effect after a single application for chronic pain prophylaxis is discussed, as opposed to the daily use of current conventional prophylactic medications. Finally, we summarize the clinical applications of BoNT-A for chronic orofacial pain therapy.