Effects of bilingualism on age at onset in two clinical Alzheimer's disease variants

Introduction: The effect of bilingualism on age at onset has yet to be examined within different clinical variants of Alzheimer's disease. Methods: We reviewed the research charts of 287 well-characterized participants with either amnestic Alzheimer's dementia or logopenic variant primary progressive aphasia (lvPPA) and identified bilingual speakers based on regular use of two or more languages and/or ability to communicate with native speakers in two or more languages. We evaluated whether bilingual speakers demonstrated a delay in age of symptom onset relative to monolingual speakers while controlling for other variables known to influence cognitive reserve. Results: A 5-year delay in age at symptom onset was observed for bilingual relative to monolingual speakers with lvPPA. This delay in onset was not observed in the amnestic Alzheimer's dementia cohort. Discussion: Bilingualism may serve as a unique cognitive reserve variable in lvPPA, but not in amnestic Alzheimer's dementia.