The paroxysmal dyskinesias.

The clinical, pathophysiological and genetic features of some of the paroxysmal movement disorders are reviewed. Paroxysmal kinesigenic choreoathetosis/dyskinesias (PKC/PKD) is a condition in which brief and frequent dyskinetic attacks are provoked by sudden movement. PKC is more common in men and can be idiopathic (commonly familial) or due to a variety of causes. The pathophysiology of PKC is uncertain but it could be an ion-channel disorder. Antiepileptic drugs particularly carbamazepine are very helpful in a large proportion of cases. Paroxysmal exercise induced dystonia (PED) is a rare disorder manifesting as episodes of dystonia mostly affecting the feet induced by continuous exercise like walking or running. Although the initial cases were familial, there is a higher proportion of sporadic cases. The pathophysiology of PED is unknown and antiepileptic drugs are generally unhelpful. In paroxysmal dystonic choreoathetosis/non-kinesigenic dyskinesias (PDC/PNKD) the attacks are of long duration and induced by variety of factors including coffee, tea, alcohol and fatigue but not by sudden movement. PDC can be idiopathic (familial or sporadic) or symptomatic due to a variety of causes. The gene for familial PDC has been linked in 2 families to chromosome 2 q close to a cluster of ion channel genes again suggesting that this disorder may also be a channelopathy. Other paroxysmal disorders include paroxysmal nocturnal dyskinesia, a form of frontal lobe epilepsy in some cases which may be familial with autosomal dominant inheritance (ADNFLE). The gene for ADNFLE in one family has been found to be a mutation in the neuronal acetylcholine receptor gene (CHRNA4) on chromosome 20q. Tonic spasms in multiple sclerosis and Sandiffers syndrome producing intermittent torticollis in infants and children are other paroxysmal movement disorders.