Decreased neck muscle strength is highly associated with pain in cervical dystonia patients treated with botulinum toxin injections

Abstract

Objectives: To compare the isometric neck muscle strength of cervical dystonia patients treated with botulinum toxin injections with that of healthy control subjects and to evaluate the association between neck strength, neck pain, and disability in these patients.

Design: Clinical cross-sectional study.

Setting: Outpatient rehabilitation and neurology clinics in a Finnish hospital.

Participants: Twenty-three patients with cervical dystonia with botulinum toxin-treated neck muscles and 23 healthy control subjects.

Interventions: Not applicable. Main outcome measures Isometric neck strength was measured by a special neck strength measurement system. Disability was measured by the Neck Disability Index, and pain and symptoms of cervical dystonia by a visual analog scale.

Results: Isometric neck strength in all directions measured was significantly lower (25%-44%) in the cervical dystonia patients than in the healthy controls. Neck pain levels reported during the strength tests (r range, -.36 to -.70) and neck pain experienced during the preceding week (r range, -.52 to -.63) were inversely associated with isometric strength results. The difference between sides in rotation strength was 35% in the patient group (P<.001), whereas no significant difference between sides was found in the healthy controls. Fifty-one percent of the patients reported moderate or severe disability. Pain, stiffness, and incorrect position of the head were the most prominent symptoms.

Conclusions: Cervical dystonia patients with botulinum toxin-treated neck muscles showed significantly lower maximal neck strength than healthy controls. The patients also had a statistically significant difference between sides in neck rotation strength. Thus, strength measures may be useful to detect disturbance in the function of the neck muscles.