Background: Few longitudinal studies evaluate differences in patterns of change of category compared to letter fluency across the spectrum of cognitive impairment. Methods: We compared change in category (animal and supermarket) and letter (F, A, S) fluency among 239 participants in 3 groups: remained cognitively normal throughout follow-up (n = 96), developed Alzheimer’s Disease (AD; preclinical AD, n = 21), and with AD at initial testing (prevalent AD, n = 122). Results: At baseline, prevalent and preclinical AD groups scored lower on animal than letter fluency. On all fluency measures, the prevalent AD declined faster than other groups (all P < .0001), and preclinical AD declined faster than unimpaired (all P ≤ .02). Overall, animal fluency declined faster than letter fluency; animal fluency declined significantly faster than letter fluency among cognitively normal and prevalent AD participants. Conclusion: Greater longitudinal declines in category compared to letter fluency are consistent with cross-sectional studies. Steeper declines on both fluency measures distinguish preclinical AD from cognitively unimpaired individuals.
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