Semantic and Phonemic Verbal Fluency Discrepancy in Mild Cognitive Impairment: Potential Predictor of Progression to Alzheimer's Disease.

OBJECTIVES: To assess the utility of verbal fluency discrepancy scores in predicting progression to Alzheimer's disease (AD) in a cohort of individuals with mild cognitive impairment (MCI). DESIGN: Case control. SETTING: Cases identified from new referrals to a memory clinic and controls identified from The Irish Longitudinal Study on Ageing. PARTICIPANTS: Of 308 individuals with MCI at baseline identified from consecutive referrals to a memory clinic and compared at with age-, sex-, and education-matched controls (n=302), 161 completed 2 years of follow-up or progressed to AD during the study period. MEASUREMENTS: Verbal fluency discrepancy (semantic-phonemic fluency) scores at baseline were calculated for each participant. Each case was followed with repeated neuropsychological measurements, and multidisciplinary consensus diagnosis was recorded. RESULTS: Mean discrepancy score for those who progressed to AD (2.7) was significantly lower than for those who retained a MCI diagnosis (4.8) and normal controls (7.7) (p<.001). Logistic regression revealed that, for each unit decrease in discrepancy score at baseline, the odds of progressing to AD were 9% greater. (Exp(B) = 1.09, p=.02) CONCLUSION: Individuals with MCI have less of a semantic advantage than those without MCI. Those with MCI presenting with a phonemic advantage at initial assessment warrant close follow-up and a high index of suspicion for progression to AD.

Preservation of the Semantic Verbal Fluency Advantage in a Large Population-Based Sample: Normative Data from the TILDA Study.

OBJECTIVES: It is widely believed that phonemic fluency is more difficult than naming exemplars from a semantic category. Normative data in this regard are scarce, and there is considerable disagreement in the literature regarding the pattern in normal ageing and neurodegenerative conditions. Our objective was to provide normative data for semantic phonemic discrepancy scores from a large sample of older adults. METHODS: A total of 5780 community-dwelling older adults were included in this prospective, longitudinal study. Discrepancy scores were calculated by subtracting phonemic fluency score from semantic fluency score for each participant. Quantile regression was used to estimate normative values stratified for age. RESULTS: Subjects did better on testing of semantic fluency. The average discrepancy score was 9.18±6.89 words, (range, -20 to 37; n=5780). At the fiftieth percentile, those in their fifth decade produced 10 more "animals" than "letter F" words. Subjects scored one word less per decade, with an average of seven more "animal" words produced by those in their eighth decade. CONCLUSIONS: Our study is the first to provide normative data and confirms that, for animal versus letter F fluency, the semantic advantage persists into later life in a population-based sample of community-dwelling older adults. Given that a majority of clinical samples have confirmed a reverse of this pattern in Alzheimer's dementia (i.e., loss of semantic advantage in Alzheimer's disease, yielding a phonemic advantage), our findings support the clinical utility of brief fluency tests and encourage further research into their use in diagnosis and prediction of progression to dementia.