Improvement of cervical dystonia: possible role of transcranial magnetic stimulation simulating sensory tricks effect.

Idiopathic cervical dystonia (ICD) is the most common form of focal dystonia. A characteristic and unique diagnostic feature is the presence of "sensory tricks", for example, a finger placed on the chin to neutralize the spasm. Although approximately 70% of patients with ICD experience effective sensory tricks, the exact mechanism of these tricks is still unknown. However, recent evidence suggests that higher sensorimotor integration processes are involved. A study using H2(15)O positron emission tomography demonstrated that the application of sensory trick stimulus, resulting in a near-neutral head position, led to an increased activation mainly of the superior and inferior parietal lobules (ipsilateral to head turn) and bilateral occipital cortex and to a decreased activity of the supplementary motor area and the primary sensorimotor cortex (contralateral to head turn). Since transcranial magnetic stimulation (TMS) is an experimental device with the ability to excite or depress the neural circuits, we hypothesize that the use of TMS of specific parameters to specific brain areas (as above) may produce an effect similar to sensory tricks resulting in the relief of spasms and the improvement of cervical dystonia.