J Mov Disord.  2016 Jan;9(1):44-49. 10.14802/jmd.15035.

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

Affiliations
  • 1Department of Physical Medicine and Rehabilitation, Central Finland Central Hospital, Jyväskylä, Finland. sirpa.mustalampi@ksshp.fi
  • 2Department of Health Sciences, University of Jyväskylä, Jyväskylä, Finland.
  • 3Department of Sports Medicine, Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.

Abstract


OBJECTIVE
To evaluate changes in the strength and mechanical properties of neck muscles and disability in patients with cervical dystonia (CD) during a 12-week period following botulinum neurotoxin (BoNT) injections.
METHODS
Eight patients with CD volunteered for this prospective clinical cohort study. Patients had received BoNT injections regularly in neck muscles at three-month intervals for several years. Maximal isometric neck strength was measured by a dynamometer, and the mechanical properties of the splenius capitis were evaluated using two myotonometers. Clinical assessment was performed using the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) before and at 2, 4, 8, and 12 weeks after the BoNT injections.
RESULTS
Mean maximal isometric neck strength at two weeks after the BoNT injections decreased by 28% in extension, 25% in rotation of the affected side and 17% in flexion. At four weeks, muscle stiffness of the affected side decreased by 17% and tension decreased by 6%. At eight weeks, the muscle elasticity on the affected side increased by 12%. At two weeks after the BoNT injections, the TWSTRS-severity and TWSTRS-total scores decreased by 4.3 and 6.4, respectively. The strength, muscle mechanical properties and TWSTRS scores returned to baseline values at 12 weeks.
CONCLUSIONS
Although maximal neck strength and muscle tone decreased after BoNT injections, the disability improved. The changes observed after BoNT injections were temporary and returned to pre-injection levels within twelve weeks. Despite having a possible negative effect on function and decreasing neck strength, the BoNT injections improved the patients reported disability.

Keyword

Muscle strength; Muscle characteristics; Disability; Neck
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