Migraine and movement disorders.

A large series of clinical and experimental observations on the interactions between migraine and the extrapyramidal system are available. Some previous studies reported high frequency of migraine in some basal ganglia (BG) disorders, such as essential tremor (ET), Tourette's syndrome (TS), Sydenham's chorea and more recently restless legs syndrome (RLS). For example, the frequency of migraine headache in a clinic sample of TS patients was found nearly fourfold more than that reported in the general population. To the best of our knowledge, no controlled studies have been conducted to determine a real association. ET and migraine headache have been considered comorbid diseases on the basis of uncontrolled studies for many years. In a recent Italian study, this comorbid association has been excluded, reporting no significant differences in the frequency of lifetime and current migraine between patients with ET and controls. Among mostly common movement disorders, RLS has been recently considered as possibly comorbid with migraine. Studies in selected patient groups strongly suggest that RLS is more common in migraine patients than in control populations, although no population-based study of the coincidence of migraine and RLS has yet been identified. The exact mechanisms and contributing factors for a positive association between migraine and RLS remain unclear. A number of possible explanations have been offered for the association of RLS and primary headache, but the three most attractive ones are a hypothetical dopaminergic dysfunction and dysfunctional brain iron metabolism, a possible genetic linkage and a sleep disturbance. More recently, the role of BG in pain processing has been confirmed by functional imaging data in the caudate, putamen and pallidum in migraine patients. A critical appraisal of all these clinical and experimental data suggests that the extrapyramidal system is somehow related to migraine. Although the primary involvement of extrapyramidal system in the pathophysiology of migraine cannot as yet be proven, a more general role in the processing of nociceptive information and/or maybe part of the complex behavioral adaptive response that characterizes migraine may be suggested.