Static Graviceptive Functions in Patients With Cervical Dystonia (CD)

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:

• the habitual head deviation (head deviation will be classified by Tsui score),
• head fixed in neutral head position (defined as 0° or no head rotation).
• 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.

Inclusion criteria

• Idiopathic CD and willing to participate on the study,
• Isolated laterocollis or laterocollis and torticollis with maximum of 15°rotation
• Aged 18-80 years,
• Under routine treatment with botulinum toxin

Exclusion criteria

Patients and Control

• History of vestibular disorders

Patients

• Torticollis with >15°rotation
• Secondary CD (structural MRI lesions, Mb. Wilson)
• Contraindication for intramuscular botulinum toxin therapy: bleeding disorder or anticoagulation therapy