Brain amyloid-β deposition, severity of subjective cognitive decline and gait speed in cognitively unimpaired oldest-old.

BackgroundGait speed slows prior to cognitive decline in clinical Alzheimer's disease (AD), and is associated with cognitive performance and biomarkers of amyloid-β (Aβ) pathology in cognitively unimpaired (CU) older adults. However, the influence of subjective cognitive decline (SCD) severity on the association between Aβ and gait speed is not known.ObjectiveWe examined the relationship among gait speed, SCD severity and Aβ deposition in CU older adults.MethodsGait speed was measured over 15-feet. Aβ deposition was quantified using Pittsburgh-B (PiB) PET, expressed in Centiloid units (CL). Severity of SCD was quantified on the Memory Functioning Questionnaire (MFQ) on measures of seriousness and frequency of forgetting, mnemonic usage and retrospective functioning. We fitted a series of linear models with gait speed as the dependent variable; and each dichotomized sub-scale of the MFQ and Aβ as independent variables, adjusting for depression, white matter hyperintensity volume and executive function.ResultsIn 58 CU individuals (mean age 85, 35% female), mean gait speed was 0.91 m/s and Aβ deposition was 36 CL. The relationship between slower gait and greater Aβ deposition showed a stronger association in those with more frequent mnemonic use (r = -0.36, p = 0.05) and with greater seriousness of forgetting (r = -0.33, p = 0.08) compared to those with lesser severity of subjective cognitive concerns (r = 0.02, p = 0.9 and r = -0.08, p = 0.7 respectively).ConclusionsThe findings indicate that in those with greater severity of SCD, association between slower gait and greater Aβ deposition is stronger, warranting longitudinal assessments of SCD severity and gait changes in preclinical AD.