BackgroundThe effectiveness of onabotulinumtoxinA (BTX-A) has been established in primary trigeminal neuralgia (TN). However, to the best of our knowledge, the efficacy of BTX-A in secondary TN has not yet been studied. ObjectiveThis study aimed to investigate the efficacy of BTX-A treatment in patients with multiple sclerosis-related trigeminal neuralgia (TN-MS) and compare the efficacy of BTX-A treatment between patients with primary trigeminal neuralgia (TN-P) and patients with TN-MS. MethodsThis was a retrospective medical record-review study. Demographic and clinical features and severity and frequency of pain before and 2 weeks after the BTX-A administration were extracted from the patient files. BTX-A was injected into the painful area subcutaneously and/or submucosally. BTX-A injections were performed by the same physician using the same methods. A reduction in severity and/or frequency of pain >= 50% was considered therapeutic efficacy. ResultsFifty-three patients were included in this study. We classified 22 (42%) as TN-P and 31 (58%) as TN-MS. Treatment with BTX-A was effective in 16 of 31 (52%) patients with TN-MS and 10 of 22 (45%) with TN-P. BTX-A treatment was less effective in patients with a history of interventional treatments and more effective in patients with concomitant continuous pain (p = 0.007; odds ratio [OR]: 0.020-0.53 and p = 0.047; OR: 0.046-0.98, respectively). ConclusionThe BTX-A treatment was found to be effective in at least half of our cohort with TN-MS. Concomitant continuous pain and history of interventional treatments to the trigeminal nerve or ganglion might be predictive factors for the efficacy of BTX-A treatment.