Researcher: Paulien de Vries, MD, PhD

Other supervisors: Nico Leenders, MD, PhD, Bauke de Jong, MD, PhD

Thesis defense: 2008

Cervical dystonia (CD) is a movement disorder characterized by sustained involuntary muscular contractions which cause repetitive twisting movements and abnormal postures of the head. CD is primarily a brain disorder. Several studies show that CD patients have abnormal brain activity not only during movement execution but also movement preparation. An important area for movement preparation is the parietal cortex where sensory information is integrated in the movement preparation plan. In CD, this parietal cortex seems to function abnormally since extra sensory information (by touching the chin or cheek) can temporarily reduce dystonia. This thesis investigated execution and preparation of movement in CD and healthy controls by letting the subjects perform and imagine a flexion/ extension movement in a normal, non-dystonic hand. Imagination of movement activates specific brain areas which are related to preparation of movement. Both tasks showed lower parietal cortex activity in CD compared to healthy controls. Induced impairment of the parietal cortex by transcranial magnetic stimulation (TMS) in healthy controls showed specific brain activation changes that were similar to brain activation patterns in CD patients without TMS. Parietal cortex TMS in CD reduced the already low activity even further and increased activity in other brain regions. These results confirm that the parietal cortex is impaired in CD. This functional impairment seems to be compensated by other brain regions during movement in normal, non-dystonic body parts. However, the electromyography study in this thesis showed that full compensation is not reached, although visually the movement looked normal. Execution of a flexion/ extension movement of a normal, non-dystonic hand in CD patients demonstrated lower muscle strength during wrist flexion and longer muscle activation during wrist extension. Nevertheless, in CD other factors besides impaired compensation mechanisms may be in play to undermine the neck movements in CD patients in such a way that it becomes dystonic.

References

• de Vries PM1, Leenders KL, van der Hoeven JH, de Jong BM, Kuiper AJ, Maurits NM. Abnormal surface EMG during clinically normal wrist movement in cervical dystonia. Eur J Neurol. 2007 Nov;14(11):1244-50. PMID: 17903212.