Letter and Semantic Fluency in Alzheimerʹs, Huntingtonʹs, and Parkinsonʹs Dementias

A pattern of semantic fluency worse than letter fluency has been presented as evidence of impaired semantic networks in “cortical” dementias (e.g., Alzheimerʹs disease), distinguishing them from “subcortical” dementias (e.g., Parkinsonʹs disease, Huntingtonʹs disease). However, there have been few systematic studies of this propositions. The present study compared Alzheimerʹs, Parkinsonʹs, and Huntingtonʹs 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. Huntingtonʹs subjects had significantly more repetition errors than all other groups, and Alzheimerʹs subjects had significantly more repetition errors than Parkinsonʹs subjects and normal controls. There were no differences in number of intrusion errors. Findings suggest that semantic fluency deficits are not unique to Alzheimerʹs dementia and may not help to differentiate between different etiologies of dementia.