Alterations in vestibular function in individuals with cervical dystonia and the effects of botulinum toxin treatment

Introduction: Individuals with cervical dystonia (CD) often report difficulty with balance and an altered perception of vertical. Previous studies have suggested a decreased proprioceptive response to stretch of neck muscle spindles in these patients, and impaired dynamic balance changes in individuals with tremor. Methods: Participants with CD were divided into three groups based on severity of tremor and dystonic position on the Toronto Western Spasmodic Torticollis Rating Scale 2 (TWSTRS2). Unaffected controls completed assessments including Fukuda, modified Romberg, and subjective visual vertical tests. Participants with CD completed the same assessments at baseline and 4 to 6 weeks following botulinum toxin treatment. Results: CD participants with marked tremor and deviation had more difficulty perceiving what was vertical as demonstrated by a greater degree off midline on the subjective visual vertical test, compared to individuals with marked tremor with minimal deviation and controls, though this was not significant after adjustment for multiple comparisons. Individuals with CD also had more difficulty maintaining balance on a compliant surface with eyes closed compared to controls on the modified Romberg test. TWSTRS2 motor severity score was significantly associated with degrees off midline on the subjective visual vertical test at baseline for CD participants, but not after botulinum toxin treatment. Conclusions: Individuals with more severe tremor and dystonic posture appear to have an altered perception of vertical associated with CD severity and that may improve following botulinum toxin treatment. Modified Romberg testing suggests that visual cues may also be important to compensate for tremor and dystonic positions found in CD.