Botulinum toxin type A versus botulinum toxin type B for cervical dystonia.

backgroundCervical dystonia is the most common form of focal dystonia. It is characterized by involuntary posturing of the head and frequently is associated with neck pain. Disability and social withdrawal are common. Most cases are idiopathic, and generally it is a life-long disorder. In recent years, botulinum toxin type A (BtA) has become first line therapy for cervical dystonia. However, not all patients respond well to BtA, and 5 to 10% become resistant to it. Botulinum toxin B (BtB) is an alternative to BtA and offers the potential to help patients who do not respond to BtA. At present there is no compelling theoretical reason why it should not be as effective as, or even more effective than, BtA.

objectivesTo compare the clinical efficacy and safety of BtA versus BtB in cervical dystonia. SEARCH STRATEGY: Studies for inclusion in the review were identified using the Cochrane Movement Disorders Group trials register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, by handsearching the Movement Disorders Journal and abstracts of international congresses on movement disorders and botulinum toxin, by communication with other researchers in the field, by searching reference lists of papers found using the above search strategies, and by contact with authors and drug manufacturer. SELECTION CRITERIA: Studies were considered eligible for inclusion in the review if they evaluated the efficacy of BtA versus BtB for the treatment of cervical dystonia. Trials must have been randomised and placebo-controlled. DATA COLLECTION AND ANALYSIS: A paper pro-forma was used to collect data from the included studies using double extraction by two independent reviewers. Each trial was assessed for internal validity by each of the two reviewers. Differences were settled by discussion. The outcome measures used included improvement in symptomatic rating scales, subjective evaluation by patients and clinicians, changes in pain scores, changes in quality of life assessments, and frequency and severity of adverse events. MAIN

resultsWe cannot give any results since we have only identified two ongoing trials and there are no preliminary results or interim analyses available for them. The full results of these trials are expected in late 2004 or 2005. AUTHORS'

conclusionsIt is currently not possible to make definitive comparisons between BtA and BtB for the treatment of cervical dystonia; uncontrolled comparisons should be regarded with suspicion.