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RESEARCH PRODUCT

Reduced Neck Muscle Strength and Altered Muscle Mechanical Properties in Cervical Dystonia Following Botulinum Neurotoxin Injections : A Prospective Study

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description

Cervical dystonia (CD) is a focal dystonia causing involuntary activation of neck and shoulder muscles resulting in abnormal, sustained and painful posturing that may lead to physical disability and social withdrawal [1]. In recent years, botulinum neurotoxin (BoNT) has become the first line therapy for CD [2]. A subjective feeling of neck weakness has been reported as one of the most common localized adverse events of BoNT [2-7]. In clinical practice, this may sometimes be reported as having difficulty keeping the head upright. Although the effects of BoNT have been widely studied [2,5], there have been no prospective studies quantifying changes in maximal isometric neck muscle strength. Objective strength measurements may help identify patients with neck weakness after BoNT injections that causes difficulties in daily living and therefore need additional strength training. Additionally, even though CD patients have frequent complaints of neck tension, only one study [8] has provided quantitative data about the effects of initial BoNT injections on the passive mechanical properties of skeletal muscle in a clinical setting, despite that measurement devices have been developed for this purpose. Myotonometers may provide an objective, non-invasive tool to quantify changes in muscle properties after BoNT injections that were previously obtained using subjective methods. The aim of this study was to evaluate the changes in neck strength, the mechanical properties of neck muscles, and disability over a twelve-week period following BoNT injections in patients with CD who had a two-year history of BoNT treatment. We hypothesized that the mechanical properties of muscle fluctuate after BoNT injection, and this fluctuation is reflected in decreased muscle power and tension, as well as disability.