Classification conundrums in paroxysmal dyskinesias: a new subtype or variations on classic themes?

Paroxysmal movement disorders are a group of heterogeneous entities that have been categorized based on their most salient features. The four classic categories of paroxysmal dyskinesias are kinesigenic, nonkinesigenic, hypnogenic, and exercise-induced. The phenotypic variability of these disorders, coupled with new insights into their possible etiologies, has made the task of classification increasingly problematic. We describe 4 cases that do not fit easily into the current classification scheme, compare them with four others recently described in the literature, and raise the question as to whether they constitute a new subtype.