Initial letter and semantic category fluency in Alzheimer's disease, Huntington's disease, and progressive supranuclear palsy.

Ten patients with dementia of Alzheimer's type, 10 patients with progressive supranuclear palsy, and 10 patients with Huntington's disease were compared on two types of verbal fluency task--namely, initial letter fluency and category (semantic) fluency. The groups were carefully matched for overall level of dementia on the dementia rating scale, and were compared with 25 age matched normal controls. The controls found letter fluency more difficult than category fluency, and this relative pattern of performance was repeated in the progressive supranuclear palsy and Huntington's disease groups, although both groups were significantly impaired on both tasks. By contrast, patients with Alzheimer's disease performed just as poorly as the progressive supranuclear palsy and Huntington's disease groups on the category tasks, but were significantly less impaired at letter fluency, performing at near normal levels on this task. From these results, it is suggested that the performances of patients with progressive supranuclear palsy and Huntington's disease relate largely to initiation and retrieval problems secondary to disruption of frontostriatal circuits, whereas in Alzheimer's disease, the poorer performance on category fluency is due principally to the breakdown of semantic knowledge, which probably reflects temporal neocortical involvement.