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

Abstract

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.

Keywords: Alzheimer's disease; mild cognitive impairment; neuropsychological assessment; verbal fluency.