Objective: To assess the safety and efficacy of Botulinum toxin (Btx) injections in essential head tremor (HT) in a multicenter, randomized, double blind, parallel-group, placebo-controlled therapeutic phase III study.

Background: While HT is not usually improved by oral treatment, local Btx A injections could be an effective and safe approach [1,2]. However studies on this topic are few and very imprecise (small samples, open studies).

Method: 120 patients with HT were recruited in 17 French hospitals and randomized in 2 groups: the “Btx” group which received injections of 75 U of Btx A or the “P” group which received injections of placebo (saline solution 0.9 %), in each splenius capitis muscles under electromyographic detection. Patients were injected 2 times spaced in 3 months at D0 and W12. At W12, the dose injected could be increased at 100 U if the first injection was ineffective. Six weeks after each injection, at W6 and W18, the clinical state of the patient was evaluated with the CGI: this parameter was considered as improved if the score was at least improved of 2 points. The severity of HT, the Fahn-Tolosa-Marin tremor rating scale (TRS), and the Essential Tremor Embarrassment Assessment (ETEA) were also evaluated. The main outcome was the CGI measured at W18.

Results: Intention to treat (ITT) analysis, with maximum bias imputation, showed that the percentage of patients with a CGI improved was significantly higher in Btx vs P groups at W18 (30.7 vs 9.1 % respectively, p=0.009) and at W6 (43.6 vs 7.3 % respectively, p<0.001). At W6, severity HT and TRS scores, sub items HT and part C, were significantly improved in Btx vs P groups (p=0.001 for severity HT, p<0.001 for TRS-sub items HT, p=0.003 for TRS-part C). At W18, these scores were not different between the 2 groups in ITT analysis but became significantly ameliorated in Btx group in per protocol analysis (p = 0.009 for severity HT, p=0.003 for total TRS).  ETEA scores were also significantly improved in Btx vs P groups at W18 (p=0.0122 respectively). Major side effects were local pain, neck weakness, headache and dysphagia.

Conclusion: Btx injections were effective to treat HT. Social embarrassment was also improved.

References: [1]. Pahwa R et al. Botulinum toxin treatment of essential head tremor. Neurology. 1995;45:822-824.
[2]. Wissel J et al. Quantitative assessment of botulinum toxin treatment in 43 patients with head tremor. Mov Disord. 1997;12:722-726.

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