A long list of symptoms present in Parkinson's disease may be targeted with botulinum toxins to alleviate the burden of disease. Studies investigated its efficacy in tremor, sialorrhea, dystonia, freezing of gait, camptocormia (bent spine syndrome), urinary dysfunction, constipation, eyelid opening apraxia, blepharospasm, and in dysphagia, a condition highly prevalent in Parkinson's disease (up to 81%) which can cause serious complications.
It might be time to reconsider botulinum toxins for tremor, as botulinum toxin injections adapted to the patients are effective in controlling tremor and at the same time avoid wrist extensor inhibition and the occurrence of weakness in the hand.
Hand tremor is a common movement disorder that may be caused by essential tremor, Parkinson's disease, or dystonia. Hand tremor may be very disabling and is often associated with an impairment of quality of life despite optimal therapy. Dr Nicki Niemann (Baylor College of Medicine, USA) stressed the fact that tremor treatment with oral drugs is often limited by lack of efficacy and systemic side effects . Invasive procedures, such as deep brain stimulation and MRI-guided ultrasound thalamotomy, are reserved for severe and disabling tremor.
Early clinical trials with botulinum toxin in essential tremor showed a clinically moderate improvement of tremor amplitude. However, relatively high rates of side effects were also seen. Benefits were limited by clinically significant weakness, particularly of extensor muscles and wrist weakness, which were attributed to the injection techniques [2,3]. With modification of the injection technique, botulinum toxin has been increasingly used for treatment in patients with focal tremor with good outcomes and favourable long-term safety [4-6].
Onabotulinum toxin A in hand tremor
Dr Niemann performed a retrospective review of patients with refractory hand tremor who had been treated with onabotulinum toxin A injections between 2010-2018 in at least two sessions. He obtained data on muscle selection, dose, and response to prior injection from 91 patients (i.e. 53 with essential tremor, 6 with Parkinson's disease, 31 with dystonia, and 1 patient with cerebellar outflow tremor) in whom tremor was optimised prior to the first onabotulinum toxin A injection. In 97.8% of the patients, forearm flexors were injected and 2.2% received injections other than the forearm flexors. EMG was used in only 5.5% of the patients, while all other patients were injected relying on surface anatomy. It was demonstrated that patients had sustained benefits during an average follow-up period of 2.5 years. In most patients, marked or moderate improvement of tremor severity and function on the peak-effect rating and global-effect rating scales was reported.
Dr Niemann concluded that by avoiding injections into forearm extensors, clinically significant wrist and finger weakness was largely avoided while tremor reduction was maintained. Onabotulinum toxin A injections were safe and effective in the treatment of hand tremor .
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- Jankovic J. Mov Disord. 2017 Aug;32(8):1131-1138.
- Mittal SO, et al. Mayo Clin Proc. 2017 Sep;92(9):1359-1367.
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- Niemann N, Jankovic J. Poster P2.28, abstract 197, TOXINS 2019, Copenhagen, Denmark, 16-19 January, 2019.
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