Pain localization and response to botulinum toxin in cervical dystonia.

[INTRODUCTION] Pain is a common symptom of cervical dystonia (CD). The mainstay of treatment of CD is botulinum toxin, which is known to have benefits in relieving pain. We aimed to characterize the locations of pain in patients with CD, and to assess what factors may predict pain reduction following botulinum toxin injection.

[METHODS] We conducted a single-center observational study of CD patients who reported pain and who received botulinum toxin treatment. On the day of their toxin injection (in the untreated state), they filled out a survey evaluating primary and secondary sites of pain as indicated on a diagram, as well as Pain Numeric Rating Scale assessing average pain over the past 24 h. Two weeks later, they filled out a follow-up survey (in the treated state) to evaluate whether location and pain intensity changed.

[RESULTS] 55 people with CD participated in the study, and 40 of them completed both surveys. Most patients reported pain localization over the posterior musculature, especially in the areas overlying superior trapezius and levator scapulae. 21 of 40 (52.5%) patients reported improvement of pain intensity by ≥ 30% in the primary site of pain. The mean improvement in pain intensity was 30.4% (SD = 32.4%), with a mean improvement on Numeric Rating Scale of 2.13 (SD = 2.02). 68% of patients received injections into or close to their primary site of pain. Using univariate linear regression, there was no clear effect of age, sex, muscles injected, or TWSTRS motor subscale on the degree of pain improvement. The locations of pain remained relatively stable in the post-treatment state.

[CONCLUSION] We confirmed that botulinum toxin is effective for treatment of pain related to CD. We also gained insight into the typical locations of pain in CD by generating a heat map, showing pain most often in the regions of upper trapezius, levator scapulae, and splenius cervicus and capitis. Although there was not a significant correlation between the site of botulinum toxin injection and pain improvement, larger studies are needed to better determine optimal treatment strategies.