Clustering and switching in semantic fluency: predictors of the development of Alzheimer's disease

The aims of the study are twofold: (1) to compare semantic fluency, clustering and switching performance among subjects with memory complaints, patients with Alzheimer Disease (AD), and healthy controls; and (2) to examine the clinical utility of the clustering/switching scoring system in the prediction of incident AD in subjects with memory complaints.

A semantic fluency task was used to compare thirty eight subjects with memory complaints, forty two AD patients and twenty five healthy controls on the total number of words generated, clustering and switching performance. Subjects with memory complaints were followed-up for a maximum period of two years and re-evaluated. They remained in the memory complaints group (twenty eight subjects) or were defined as probable AD (ten subjects).

AD patients generated fewer correct words (p < 0.001) and showed a reduction in clustering (p = 0.008) and switching (p < 0.001). Subjects with memory complaints showed a significant reduction in correct words (p < 0.001) and clustering performance (p = 0.008) compare to controls. In the first evaluation, the subgroup of patients who converted to AD at follow up produced less correct words (p < 0.01) and smaller clusters (p = 0.007) than the subgroup who did not become demented. There were no differences in switching between these two subgroups. AD development was better predicted by cluster size than by the total number of words generated or by switching.

Subjects with memory complaints and AD patients have an alteration in both qualitative and quantitative aspects of semantic fluency. A clustering analysis could enhance the reliability of early AD diagnosis.