Dosage of botulinum toxin in patients undergoing treatment for hemifacial spasm: is there modification during follow-up?

Background The movement disorder known as hemifacial spasm is characterized by involuntary contractions of the muscles that are innervated by the facial nerve. The treatment of choice for this condition is botulinum toxin injections. Objective To analyze the botulinum toxin dosage in patients undergoing treatment for hemifacial spasm during a 14-year period. Methods A retrospective study of medical records from patients treated at the Neurology Service of Hospital Universit & aacute;rio Onofre Lopes, Universidade Federal do Rio Grande do Norte, from 2010 to 2024, was performed. Results A total of 151 patients met the inclusion criteria. The dose of botulinum toxin revealed a statistically significant increase during the first 3.46 years of follow-up. In the long-term, a trend toward dose stabilization was identified. The median latency for the onset of effect was 4 days, while the median duration of effect was 3 months. All side effects were temporary, with the most common being hemifacial weakness (17.9%) and palpebral ptosis (3.3%). Most patients presented primary hemifacial spasm (88.1%), with a neurovascular conflict identified in 24.1% of cases. Conclusion The increase in botulinum toxin dosage during the first years may be explained by dosage adjustment to control hemifacial spasm with the lowest possible doses. A prolonged interval between applications may also be associated with this increase. Dose stabilization tends to be achieved over time, indicating disease control.