Memory decline in elderly with cerebral small vessel disease explained by temporal interactions between white matter hyperintensities and hippocampal atrophy

Background: White matter hyperintensities (WMH) constitute the visible spectrum of cerebral small vessel disease (SVD) markers and are associated with cognitive decline, although they do not fully account for memory decline observed in individuals with SVD. We hypothesize that WMH might exert their effect on memory decline indirectly by affecting remote brain structures such as the hippocampus. We investigated the temporal interactions between WMH, hippocampal atrophy and memory decline in older adults with SVD. Methods: 503 participants of the RUNDMC study underwent neuroimaging and cognitive assessments up to 3 times over 8.7 years. We assessed WMH volumes semi-automatically and calculated hippocampal volumes (HV) using FreeSurfer. We used linear mixed effects models and causal mediation analyses to assess both interaction and mediation effects of hippocampal atrophy in the associations between WMH and memory decline, separately for working memory (WM) and episodic memory (EM). Results: Linear mixed effect models revealed that the interaction between WMH and hippocampal volumes explained memory decline (WM: beta=0.067; 95%CI[0.024–0.111]; p<0.01; EM: beta=0.061; 95%CI[0.025–0.098]; p<0.01), with better model fit when the WMH*HV interaction term was added to the model, for both WM (likelihood ratio test, X2(1)=9.3, p<0.01) and for EM (likelihood ratio test, X2(1)=10.7, p