Adverse events with botulinum toxin treatment in cervical dystonia: How much should we blame placebo?

[INTRODUCTION] Botulinum toxin (BoNT) is the first line therapy for cervical dystonia (CD), with most patients receiving many treatment sessions, and so come to recognize and expect the benefits and harms of BoNT, making it difficult to separate which adverse events (AEs) are driven by BoNT and which come from patients' expectations.

[METHODS] Using the results of three Cochrane systematic reviews of randomized controlled trials (RCTs) we pooled results to calculate the risk of general and specific AEs associated with BoNT, and the proportion of AEs that cannot be pharmacologically attributed to BoNT.

[RESULTS] Fifteen RCTs, enrolling 1604 patients, were included. BoNT was associated with an increased risk of AEs, but 79% of this increased risk cannot be pharmacologically attributed to BoNT.

[CONCLUSIONS] Patients with CD attach a considerable expectation of harm due to BoNT, reflected in the large proportion of non-pharmacologically-mediated AEs.