Cognitive Function And Neuroimaging Feature In Patients With Late Life Depression With Olfactory Impairment

BackgroundLate life depression(LLD)refers to patients with major depressive episode over 55 years of age.It is of great significant to accurately assess depressive symptoms and cognitive function of LLD as well as to identify patients with early Alzheimer’s Disease(AD)from normal aging among LLD,which may provide opportunities for carring out early intervention and reducing disease burden.However,limitations such as time-consuming,invasive and high cost hinder the widespread use of the current assessment tools.Olfactory function has been proved to correlate with depressive symptoms,cognitive function and risk of developing AD,but what role may olfactory testing play in assessing LLD remains unclear.MethodsOne hundred and six patients with LLD,37 patients with AD and 63 patients with amnestic mild cognitive impairment were consecutively recruited from May-2016 to March-2017 in Guangzhou Brain Hospital,and the 57 normal controls were recruited from communities.Each subject underwent comprehensive assessments,including demographic and clinical evaluations,olfactory function tests,neuropsychological assessments and neuroimaging examinations.Olfactory function tests included olfactory threshold and olfactory identification.Neuropsychological assessments included global cognitive function,memory,language,executive function,attention,visual space and depressive symptoms.Neuroimaging data of olfactory areas were acquired using Philips 3.0T MR systems.Structural analyses were performed by drawing and voxel-based morphometry(VBM),while rest-state functional analyses were performed by Functional Connectivity(FC)and Amplitude of Low-Frequency Fluctuation(ALFF).ResultsFactorial design analysis showed olfactory identification was a trait marker of LLD associated with cognitive function,and olfactory threshold was a state marker of LLD associated with depressive symptoms.Partial correlation analysis showed olfactory identification was negatively correlated with global cognitive function,memory and language scores(P<0.05),but no significant correlation was found between olfactory threshold and neuropsychological test scores in LLD.Multiple liner regression analysis showed olfactory identification was negatively correlated with memory scores(β=0.506,P<0.001).LLD with intact olfactory identification had better global cognitive function and memory performance than LLD with olfactory identification impairment,and their language function were relatively intact.Neuroimaging abnormalities were found in peripheral and central olfactory system(Reduction of volume of olfactory bulb,medial temporal lobe,insula etc;hyperactivity of medial temporal lobe,insula and inferior frontal gyrus;disconnection of left insula and inferior frontal gyrus),while the only neuroimaging abnormalities found in LLD with intact olfactory identification was the reduction of left olfactory bulb volume.ConclusionsOlfactory test may serve as a simple,easy,noninvasive and objective tool for assessing the cognitive function and depressive symptoms of LLD,that olfactory threshold associates with depressive symptoms and olfactory identification correlates with cognitive function(especially memory).Impairments were merely found in olfactory bulb in LLD with intact olfactory identification,but found in olfactory bulb and olfactory cortex in LLD with olfactory identification impairment.LLD with olfactory identification impairment showed AD-like behavioral and neuroimaging features in our study,follow-up studies are needed to confirm whether they are patients with early AD.