Botulinum toxin type A therapy for cervical dystonia.

BACKGROUND Cervical dystonia is characterized by involuntary posturing of the head and frequently is associated with neck pain. Disability and social withdrawal are common. In recent years, Botulinum toxin Type A (BtA) has become the first line therapy. However its true efficacy, in particular the potential effect size, is still unclear. OBJECTIVES To determine whether botulinum toxin (BtA) is an effective and safe treatment for cervical dystonia. SEARCH STRATEGY We searched the Cochrane Movement Disorders Group trials register (June 2003), the Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 3, 2003, MEDLINE (1977 to June 2003), EMBASE (1977 to June 2003) and reference lists of articles. We also contacted drug manufacturers and researchers in the field. SELECTION CRITERIA Randomised studies comparing BtA with placebo in adults with cervical dystonia. DATA COLLECTION AND ANALYSIS Two reviewers independently assessed trial quality and extracted data. Study authors were contacted for additional information. Adverse effects information was collected from the trials. MAIN RESULTS We found thirteen high quality eligible studies. They were short term (6 to 16 weeks). Eight trials, enrolling 361 patients, used the BtA formulation Botox(r) and five, enrolling 319 patients, used the BtA formulation Dysport. The dose and technique of administration varied significantly between studies.Meta-analysis showed statistically and clinically significant improvements on objective rating scales: (Peto OR 4.31; 95% confidence interval (CI) 2.68 to 6.94) and subjective rating scales (Peto OR 6.58; 95% CI 4.55 to 9.54); and for pain relief in subjective scales (Peto OR 11.92; 95% CI 6.32 to 22.5). However, for many of the outcomes, we could use data from only a few studies. Only adverse events clearly associated with the mechanism of action of BtA were more frequent in the treatment group. These included neck weakness, dysphagia, dry mouth/sore throat and voice changes/hoarseness. Sub-group and sensitivity analyses showed a clear dose-response relationship for subjective and objective benefit and for frequency and severity of adverse events. Indirect comparisons between trials that used Dysport against placebo and trials that used Botox against placebo showed no significant differences between Dysport and Botox in terms of benefits or adverse events. AUTHORS' CONCLUSIONS A single injection cycle of BtA is effective and safe for treating cervical dystonia. Enriched trials (using patients previously treated with BtA), suggest that further injection cycles continue to work for most patients.