A longitudinal study of quantitative and qualitative features of category verbal fluency in incident Alzheimer's disease subjects: results from the PAQUID study.

Category fluency tests were administered at baseline and after 3 and 5 years on two subgroups of subjects from a population-based cohort of elderly subjects: 52 cases of incident possible and probable Alzheimer's disease (AD) and 104 age- and education-matched subjects who remained nondemented. Quantitative and qualitative features of category fluency were assessed to determine how changes occur within 5 years of the diagnosis of AD. Consistent with previous results, we found that the number of words produced on this task was already significantly lower 5 years before the diagnosis in subjects with incident AD as compared with subjects who did not become demented. However, the rate of repetitions only significantly increased in AD subjects at the time of diagnosis, and the rate of intrusions remained low and not significantly different between the two groups. Thus, it is concluded that dysfunction in cognitive processes underlying repetitions and intrusions in verbal fluency tasks, such as inhibitory processes and working memory, may not be the main cause of the very early deficit in verbal fluency occurring in AD.