Prevalence and correlates of category versus letter fluency discrepancies in Alzheimer's disease

Alzheimer's disease (AD) patients typically exhibit greater category than letter fluency impairment, but the prevalence of this discrepancy has not been studied in a large group of patients. In the present study of 217 AD patients, we found that 145 subjects (66.8 %) demonstrated the expected pattern of better letter fluency (FAS test, i.e, generating as many words as possible in 1 minute beginning with "F", "A," and "S") than category fluency (animal generation). However, an unexpectedly large group of patients exhibited the opposite pattern of category fluency equal to or better than letter fluency (n = 72, 33.2%). Paired t-tests between groups revealed no significant differences on demographic variables such as age, gender, education level, or duration of illness. However, the smaller group exhibiting the unexpected fluency pattern exhibited significantly higher Mini-Mental State Examination (MMSE; Folstein, Folstein, & McHugh, 1975) scores compared to the larger group. Comparisons were made between group performance on other neuropsychological tasks, using MMSE performance as a covariate, but no significant differences were found. Therefore, the present results do not offer strong support for the neuropsychological (and possibly neuroanatomical) distinctiveness of the two fluency subgroups.