Secondary causes of paroxysmal dyskinesia.

PxD are sudden, episodic, involuntary movement disorders that may include any combination of dystonia, chorea, athetosis, or ballism. The majority of reported cases are familial or idiopathic; however, there have been several reports of secondary PxD. We report 20 new cases of secondary, non-psychogenic PxD, and review 130 cases reported in the literature. The results suggest that although PxD is a rare disorder, secondary forms may be more common than previously recognized, accounting for 26% of all cases in our series. Secondary cases are notable for their variability in age of onset, the presence of both kinesigenic and non-kinesigenic symptoms in some patients, the prevalence of sensory precipitants, and most importantly, the reversal of symptoms when the underlying etiology is treated in some patients. In addition to MS, other causes to be considered in patients presenting with PxD include cerebral vascular insufficiency and stroke, trauma, metabolic abnormalities, and CNS infections. Awareness of the association of these etiologies with secondary PxD will permit prompt diagnoses and appropriate interventions. Potential pathophysiologic mechanisms including loss of inhibition or primary neuronal hyperactivity are discussed. In addition, recent hypotheses regarding channelopathies in relation to PxD are presented.