Cognitive impairment in "Other" movement disorders: hidden defects and valuable clues.

There is a group of less-common movement disorders in which a clear cognitive phenotype coexists alongside the motor abnormality, and the recognition of this co-occurrence is essential to diagnose these disorders in an early phase. Examples include chorea-acanthocytosis, Niemann-Pick type C, some dominant ataxias, and pantothotenate kinase-associated neurodegeneration. However, also, in some more-common movement disorders, such as primary dystonia and essential tremor, of which the perception is that these have a more or less pure motor phenotype, cognitive deficits are commonly present, although it is not clear whether these deficits-which may be mild in the more "pure" motor disorders-have a functionally relevant impact. In both scenarios, disruption of relevant frontal-subcortical loops appears to be key, with the striatum and cerebellum as important (but not exclusive) nodes.