Letter and semantic fluency in Alzheimer's, Huntington's, and Parkinson's dementias.

A pattern of semantic fluency worse than letter fluency has been presented as evidence of impaired semantic networks in "cortical" dementias (e.g., Alzheimer's disease), distinguishing them from "subcortical" dementias (e.g., Parkinson's disease, Huntington's disease). However, there have been few systematic studies of this propositions. The present study compared Alzheimer's, Parkinson's, and Huntington's disease subjects with mild dementia to each other and to matched normal controls on letter and semantic fluency tasks. Results revealed parallel semantic/letter fluency patterns for all groups, suggesting that there is no unique pattern of semantic/letter fluency deficits for "cortical" or "subcortical" dementias. Qualitative errors (repetitions, intrusions) were also evaluated. Huntington's subjects had significantly more repetition errors than all other groups, and Alzheimer's subjects had significantly more repetition errors than Parkinson's subjects and normal controls. There were no differences in number of intrusion errors. Findings suggest that semantic fluency deficits are not unique to Alzheimer's dementia and may not help to differentiate between different etiologies of dementia.