Responsiveness to botulinum toxin type A in muscles of complex regional pain patients with tonic dystonia
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Tonic dystonia of the limbs in complex regional pain syndrome (CRPS) is associated with considerable disability. Treatment options are scarce. Botulinum toxin (BoNT) is sometimes used, but the effect is often said to be disappointing. However, this notion stems from case reports and clinicians’ opinions but has never been formally studied. We therefore investigated responsiveness to BoNT in CRPS patients with tonic dystonia. We injected the extensor digitorum brevis (EDB) muscle with BoNT-A in 17 patients with CRPS and tonic dystonia to compare the response between affected and unaffected legs. We also investigated the right legs of 17 healthy controls. Responsiveness was defined as a decrease of the amplitude of the compound muscle action potential (CMAP) of >20 % from baseline 2 weeks after BoNT-A injection. We controlled for a temperature effect on BoNT efficacy by measuring skin temperature hourly directly above the EDB muscle in the first 2 weeks. CMAP amplitude decreased >20 % after injection on the affected side in 16 of 17 CRPS patients, similar to the response in unaffected legs (12/13) or legs of controls (17/17). The degree of CMAP reduction was significantly smaller in patients than in controls (56.0 ± 22.3 vs. 70.6 ± 14.6 %; p = 0.031). This may be due to a lower physical activity level and a greater difficulty to localize the EDB muscle properly in affected legs. The decrease in CMAP amplitude was not related to skin temperature. Contrary to the prevailing opinion, BoNT-A has a normal, although perhaps slightly lower efficacy in CRPS patients with dystonia.
KeywordsComplex regional pain syndrome Tonic dystonia Botulinum toxin Non-responsiveness
This study is part of TREND (Trauma RElated Neuronal Dysfunction), a Dutch Consortium that integrates research on epidemiology, assessment technology, pharmacotherapeutics, biomarkers, and genetics on CRPS type 1. The consortium aims to develop concepts on disease mechanisms that occur in response to tissue injury, its assessment, and treatment. TREND is supported by a grant of the Dutch Ministry of Economic Affairs (BSIK03016).
Conflict of interest
JS, JGvD, JM and JJvH have nothing to disclose. JK has received an unrestricted research grant from Ipsen Pharmaceutical and Allergan, inc. for studies and teaching workshops on dystonia and from Ipsen to finance a specialized dystonia nurse. DD has received compensation for consultancies from Allergan, Ipsen, Merz, Solstice/Eisai and is share holder of Allergan. None of the companies above had a role in study design, collection, analysis, interpretation of data, in the writing of the report and in the decision to submit the paper for publication.
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