Static Graviceptive Functions in Patients With Cervical Dystonia (CD)
Condition: Cervical Dystonia
MeSH terms: Dystonia; Dystonic Disorders; Torticollis
Study type: Observational

Summary: 
      The purpose of this experimental pilot study is to test the effect of normalization of the
      head position on the sense of balance at patients with cervical dystonia under routine
      botulinum toxin treatment.
    

Detailed description: 
      Background:

      The pathophysiological mechanism of cervical dystonia remains unclear. Affection of static
      graviceptive function has been shown in these patients by measuring the Subjective Visual
      Vertical (SVV). Healthy subjects, tested with voluntary head tilt, would tilt SVV in the
      opposite direction of the head. (Müller "E" effect), whereas patients with cervical dystonia
      set SVV close to true upright with a minimal deviation toward head-tilt. The mechanism of
      this change in otolith activity in patients with cervical dystonia is still unknown. When
      treated with botulinum toxin, head deviation will be reversed during a period of approximate
      6-9 weeks, with a first peak of action after approximate 3 weeks.

      Aim

      The aim of this study is to investigate the effect of normalization of the head position
      under routine intramuscular botulinum toxin application in the cervical muscles (screening, 3
      weeks and 9 weeks after injection) on static graviceptive function in patients with cervical
      dystonia.

      Rationale

      To our knowledge, the effect of botulinum toxin therapy on static otolith function in
      patients with cervical dystonia has never been evaluated. This study may provide new
      informations on the neural plasticity of the vestibular system and may contribute to the
      understanding of pathophysiological mechanisms of cervical dystonia. Accordingly, it may help
      developing new treatment strategies for this disease.

      Primary hypothesis

      There is a difference of at least 6 degrees in subjective visual vertical of patients with CD
      tested in habitual head position at study inclusion and 3 weeks after injection of Botulinum
      Toxin.

      Study design

      Subjective visual vertical will be tested in Patients with CD, who are pre-treated with
      botulinum toxin and show a good treatment response.

      Patients SVV will be assessed before routine botulinum toxin injection (on day of injection),
      3 and 9 weeks after injection. For control, SVV will be assessed in normal subjects.

      SVV assessment

      SVV will be performed by the patient and control while sitting upright in a dark room in
      different head positions, the head is fixed using a head holder.

      In CD patients, SVV will be assessed in different head positions:

        1. the habitual head deviation (head deviation will be classified by Tsui score),

        2. head fixed in neutral head position (defined as 0° or no head rotation).

        3. ear deviated 15° and 30° to ipsilateral and contralateral side, respectively, starting
           at habitual head deviation

      SVV in normal subject, with

      A) head fixed in neutral position (defined as 0° or no head rotation),

      B) ear deviated 30° to the left,

      C) ear deviated 30° to the right,

      D) ear deviated 15° to the left,

      E) ear deviated 15° to the right, will be assessed.
    

Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        outpatient botulinum toxin clinic of the department of neurology, medical university of
        Vienna healthy subjects, residents of vienna
      
Keywords: Cervical dystonia; torticollis spasmodicus; botulinum toxin; Subjective visual vertical (SVV); SVV; static graviceptive function