Botulinum Toxin Type A in Trigeminal Neuralgia Treatment: A Case Series and Literature Review

Trigeminal neuralgia (TN) stands as a common neuropathic pain disorder. Clinically, it manifests with episodes characterized by unilateral electric shock-like or knife-like pain that can involve one or more divisions of the fifth cranial nerve. Botulinum neurotoxin type A (BoNT-A) is a neurotoxin that has demonstrated analgesic effects in neuropathic pain and positive benefits in the treatment of refractory idiopathic TN. In this paper, we aim to describe the clinical outcomes and characteristics of a series of patients with TN who have undergone BoNT-A treatment within our clinical setting. Additionally, we aim to conduct a narrative review focusing on the use of BoNT-A in the management of TN. We present a case series of four patients diagnosed with idiopathic TN who underwent evaluation and treatment at our Neurotoxin Clinic from 2015 to 2023. BoNT-A was administered for the management of refractory idiopathic TN, and retrospective data collection was conducted. Patients had a confirmed diagnosis of idiopathic TN, determined through prior normal MRI and electrophysiological tests. The mean age was 46 years (range: 40-53 years), with TN onset occurring after the age of 40 years in all cases. The average time since TN onset was 11 years, and the average follow-up time was 6.25 years. Onabotulinumtoxin-A (ONA/A) was the BoNT-A formulation used, and the number of treatments during the follow-up period ranged from 12 to 37, with a mean of 23.75 injections. At six weeks post-injection, all patients underwent systematic reevaluation, assessing latency time, clinical response, and adverse reactions. Outcomes were quantified using a 0-10 cm Visual Analog Scale (VAS) for pain intensity and the mean frequency of pain attacks per day. Flexible injection intervals were adjusted based on each patient's individual response duration. The mean improvement of pain severity on the VAS was 3.72 cm, and the mean reduction in the number of pain attacks per day was 77.32%. The average latency until the onset of treatment effect was 9.5 days, and the average duration of treatment effectiveness was 15.26 weeks. Adverse reactions were exhibited in two patients but with a low degree of severity. We also conducted a narrative review focusing on the use of BoNT-A in the management of TN. The review included randomized, double-blind, placebo-controlled trials (RCT) published between January 2012 and December 2023. Data from the four included RCTs favored the use of BoNT-A. Overall, attack frequency and pain severity were reduced one to two weeks after injections, and treatment demonstrated efficacy throughout the study follow-up until 12 weeks, as also happened in our case series. BoNT-A doses ranged from 25 U to 75 U. Based on the available evidence, BoNT-A seems to be effective and safe in the treatment of refractory idiopathic TN for up to 12 weeks. Repeated injections may be safe and maintain treatment effectiveness. The optimal dose and the duration of treatment effectiveness remain uncertain. Further studies are necessary to provide a more comprehensive understanding of BoNT-A in the treatment of TN.