Phonemic Verbal Advantage in Mild Cognitive Impairment May Predict Risk for Alzheimer Disease

Verbal fluency measures and individual semantic and phonemic fluency measures demonstrate potential for differentiating patients with mild cognitive impairment (MCI) whose impairment will progress to Alzheimer disease from those whose impairment will not progress to Alzheimer disease, according to the results of a study published in the Journal of the American Geriatric Society.

Roisin M. Vaughan, MB, of the Mercer’s Institute for Research on Ageing at St. James’s Hospital in Dublin, Ireland, and colleagues identified cases from new referrals to a memory clinic and controls from The Irish Longitudinal Study on Ageing. The study included 308 individuals with MCI at baseline and 302 control individuals matched for age, sex, and education level. Of the total 610 participants, 161 completed 2 years of follow-up or had disease progression to Alzheimer disease during the study period.

The investigators calculated verbal fluency discrepancy (semantic-phonemic fluency) scores at baseline for each participant. Each person with MCI at baseline was followed up with repeated neuropsychological testing and multidisciplinary consensus diagnosis was recorded. Semantic verbal fluency tests measure retrieval of words in a specific category (eg, flowers), whereas phonemic fluency tests measure retrieval of words starting with a specified letter of the alphabet. In normal aging, performance is usually better with semantic memory than with phonemic memory. Temporal lobe lesions, such as those found in Alzheimer disease, result in greater impairment in semantic fluency than in phonemic fluency.

Mean discrepancy score for those whose disease progressed to Alzheimer disease (2.7) was significantly lower than for those who retained an 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 progression to Alzheimer disease were 9% greater (P =.02).

The authors contend that these results suggest that individuals with a phonemic advantage are more likely to have progression to Alzheimer disease than those with a semantic advantage at baseline. They further added that use of a cut-off of 0 for the discrepancy score (those who have a phonemic advantage) gives a 94% specificity in predicting whose disease will progress to Alzheimer disease, but only a 28% sensitivity, and therefore results in a high rate of false negatives.

The authors concluded that those with a phonemic advantage at baseline should be followed more closely with a higher index of suspicion for progression to Alzheimer disease.

Reference

Vaughan RM, Coen RF, Kenny R, Lawlor BA. Semantic and phonemic verbal fluency discrepancy in mild cognitive impairment: potential predictor of progression to Alzheimer’s disease [published online March 23, 2018]. J Am Geriatr Soc. doi:10.1111/jgs.15294