Evaluation of the effects of botulinum toxin therapy on the clinical characteristics of pain and pain threshold value in patients with primary cervical dystonia

Abstract

Objective: In 70% of patients with cervical dystonia (CD), the clinical presentation includes the symptom of pain. In this study, we aimed to define the types and clinical characteristics of the pain and to investigate whether this pain is a result of central sensitization by evaluating pre- and post-botulinum toxin (BoNT) treatment pain threshold values using electrical stimulation.Methods: The study enrolled a total of 35 patients with CD who received BoNT therapy. The patients were evaluated using the pain evaluation scale and Unified Dystonia Rating scale (UDRS) before and after BoNT therapy. The pain threshold values obtained from dystonic muscles, the contiguous or contralateral muscle without dystonic activity and a normal reference muscle with distant localization were recorded through electrical stimulation with EMG guidance, and all values obtained before and after BoNT therapy were compared.Results: No difference was found between the pain threshold values obtained from dystonic muscles before and after treatment. While no difference was observed across genders or VAS groups in terms of pain threshold values, the UDRS (duration and motor severity factor) scores showed significant decreases after treatment with BoNT in patients with painful dystonia and in patients with painless dystonia.Conclusions: The absence of a difference in pre- and post-BoNT treatment pain threshold values in dystonic muscles might be explained by the absence of central sensitization. Pain relief in dystonic patients might occur secondary to decreases in dystonic muscle contractions.