Phonemic Fluency in pathologically confirmed Alzheimer’s disease (AD) versus AD with Lewy Bodies

Background Although Alzheimer’s Disease (AD) and Lewy Body Disease (LBD) have distinct underlying pathologies, the clinical differentiation of these disorders remains challenging, particularly AD versus mixed AD/LBD. Previous studies have shown that patients with mixed AD/DLB can have lower total output phonemic fluency than patients with AD. Examining the qualitative features of fluency performance may offer an even more sensitive approach to detecting group differences. One potentially useful measure is the ability to sustain generation of words over time; that is, whether a participant continues producing words across the full 60 seconds, or whether their responses “drop off”. A “drop off” in verbal generation on fluency tasks has previously been reported in Mild Cognitive Impairment due to AD. We assessed whether this qualitative phonemic fluency score would differ between autopsy confirmed AD versus mixed AD/DLB or DLB. Method Participants with postmortem pathological diagnoses of AD (n = 15) and DLB (mixed or pure DLB; n = 8) were included in the present study. Participants completed phonemic fluency task at their baseline visit as part of a neuropsychological battery of tests. Participants were asked to generate as many words as possible that start with a given letter in one minute across three trials (i.e., C, F, L). The drop off in phonemic fluency over time was calculated by dividing the number of words produced in the second half of the test (i.e. second 30‐second interval) by the total number of words generated across 60 seconds. Group differences were analyzed using a one‐way analysis of variance (ANOVA). Result Whereas total CFL score did not differ in this sample (p = .21), patients with DLB produced a significantly higher proportion of words in the second half of the CFL test (M = 0.40; SD = 0.14), compared to patients with pure AD (M = 0.27, SD = 0.10), p = 0.016. Conclusion Novel scoring of the CFL test may help to differentiate cases with pure AD and cases with DLB pathology. In the current study, pure AD patients had more difficulty in sustaining word generation over 60 seconds. Future research should continue to look at different ways to score and analyze neuropsychological assessments to improve early differential diagnosis.