Diagnostic Utility of Multi-Domain Language Measures Across the Alzheimer Disease Continuum.

Objectives: Alzheimer's disease (AD) progresses from a cognitively unimpaired stage through mild cognitive impairment (MCI) to dementia. Because language impairment often emerges before dementia, it is a candidate marker of disease stage. Yet the standard batteries of large AD research cohorts rely on a narrow set of tests that mainly evaluate the lexical-semantic domain (i.e., picture naming and verbal fluency), leaving other language domains, such as semantic memory, phonology, morphosyntax, and single-word reading, rarely assessed. We evaluated the diagnostic utility of standard and specialized language tests for distinguishing amyloid-positive MCI and dementia of the Alzheimer's type (DAT) from healthy controls (HC) and from each other. Methods: We included 286 participants from the National Alzheimer's Coordinating Center (125 HC, 53 MCI Aβ+, 108 DAT Aβ+) assessed with three standard tests from UDSv3 (semantic fluency, letter fluency, and Multilingual Naming Test [MINT]) and nine specialized tests from the FTLD Module (regular and irregular word reading, semantic word-picture matching, semantic associates, Northwestern Anagram Test - Short Form [NAT-S], Northwestern Naming Battery noun and verb naming, sentence repetition, and sentence reading). For each test, the area under the receiver operating characteristic curve (AUC) was computed for DAT vs. HC, MCI vs. HC, and DAT vs. MCI, and AUCs were compared between tests with DeLong's test. Results: Eight of 12 measures reached acceptable discrimination (AUC ≥ .700) for DAT vs. HC, five for MCI vs. HC, but only semantic fluency and NAT-S for DAT vs. MCI. Semantic fluency showed the highest discrimination in each contrast, though it did not significantly outperform the NAT-S for MCI vs. HC or DAT vs. MCI. MINT, letter fluency, and irregular word reading reached clinically meaningful accuracy in distinguishing MCI and DAT from HC, but not DAT from MCI. The remaining specialized tests reached it only for DAT vs. HC, or not at all. In a post hoc regression, adjusting for cognitive flexibility and working memory attenuated group differences; the DAT difference was no longer significant, whereas the MCI difference remained significant. Discussion: Semantic fluency was the strongest single language marker across the AD continuum. Among specialized tests, NAT-S was the most informative, challenging the view that syntax is spared in early AD. Its performance was partly explained by executive function, mainly in DAT, whereas a residual morphosyntactic component remained in MCI, and several specialized tests were limited by ceiling effects. Clinically, the NAT-S may complement semantic fluency for staging, and specialized tests may help characterize heterogeneous language profiles in MCI and DAT.