A Cochrane review [Abstract] 1 included 13 high quality studies with a total of 680 subjects. The studies compared Botulinum toxin type A (BtA) with placebo and were of short term 6 to 16 weeks. The dose and technique of administration varied significantly between studies. There were statistically and clinically significant improvements on objective rating scales: (OR 4.31; 95% CI 2.68 to 6.94) and subjective rating scales (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, data from only a few studies could be used. Sub-group and sensitivity analyses showed a clear dose-response relationship for subjective and objective benefit and for frequency and severity of adverse events. 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.
Another Cochrane review [Abstract]2 on Botulinum toxin type B (BtB) included 4 studies, with a total of 441 subjects. Studies were short term (16 weeks) employing a single BtB injection session using doses between 2500 U and 10 000 U. All patients included had previously received BtA. Three studies excluded participants known to have poorer response to Bt treatment. BtB was associated with an improvement of 14.7% (95% CI 9.8% to 19.5) as assessed by investigators, with reduction of 6.8 points in the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS-total score) at week 4 after injection (95% CI 4.54 to 9.01). MD in TWSTRS-pain score at week 4 was 2.20 (95% CI 1.25 to 3.15). Both participants and clinicians reported an improvement of subjective clinical status. BtB-treated patients had a 7.65 (95% CI 2.75 to 21.32) and a 6.78 (95% CI 2.42 to 19.05) increased risk of treatment-related dry mouth and dysphagia, respectively. There was no clear-cut dose-response. However, duration time until return to baseline TWSTRS-total score and risk of dry mouth and dysphagia were greater in patients treated with higher BtB doses. Subgroup analysis showed a higher improvement with BtB among BtA-non-responsive participants. There are no data from RCTs evaluating repeated BtB injection cycles, optimal treatment intervals and doses, usefulness of guidance techniques for injection, and impact on quality of life.
The third Cochrane review [Abstract]2 included 3 RCTs with a total of 270 subjects.Two studies enrolled only patients with a known positive response to BtA treatment. All trials evaluated the effect of a single treatment using doses from 100 U to 250 U of BtA and 5000 U to 10,000 U of BtB.There was no difference between the two types of Bt in terms of overall efficacy, with a mean difference of -1.44 (95% CI -3.58 to 0.70) points lower on TWSTRS for BtB-treated participants, measured at 2 to 4 weeks after injection. The overall risk for adverse events was also not different between Bt's (BtB versus BtA RR 1.40; 95% CI 1.00 to 1.96). However, treatment with BtB was associated with an increased risk of sore throat/dry mouth (RR 4.39; 95% CI 2.43 to 7.91; 2 studies, n=212). Treatment-related dysphagia was not different between BtA and BtB (RR 2.89; 95% CI 0.80 to 10.41; 3 studies, n=249).
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