Letter and category fluency in Alzheimer's disease: a prognostic indicator of progression?
This study investigated differential patterns of performance by 40 Alzheimer's disease (AD) patients on standardised letter and category fluency tests. The performance of 24 age and education matched controls was used to classify patients as relatively more letter fluency impaired (L < C, n = 15) or more category fluency impaired (C < L, n = 25), and clinical features distinguishing these patient subgroups were investigated. Category performance was equally impaired in both patient subgroups, whereas the L < C subgroups were particularly impaired on letter fluency. The subgroups differed significantly in duration of illness (24 months for L < C group, 47 months for C < L group; t = 2.69, p = 0.01) but did not differ in global dementia severity, age, education, general language ability, or functional status. Data on annual rate of change (ARC) on the Mini-Mental State Examination were available for 26 patients. While not statistically significant, subgroup ARC differences were suggestive of more rapid decline in the L < C patients, consistent with the finding of shorter duration of illness in this group. Word fluency tests may have potential as early predictors of rate of progression in AD.