Olfactory Deficit and Hippocampal Volume Loss for Early Diagnosis of Alzheimer’s Disease.

Background: To verify the role of olfactory test and volumetric MRI measure of hyppocampus to predict conversion from mild cognitive impairment (MCI) to Alzheimer’s Disease (AD) Methods: 18 patients with amnestic MCI (55 to 85 years old, mean age 68.0563.5 years, 9 women and 9 men), broadly defined, were followed at 12-months. Olfactory function was evaluated with the Sniffin’ Sticks Extended Test (SSET). The SSETemploys 112 felt-tip pens to evaluate odor threshold, discrimination and identification. The total score (TDI) classifies subjects in normosmic, hyposmic and anosmic. Brain MRI was acquired on a single GE 1 T unit (Gyroscan NT; Philips Medical Systems, Best the Netherlands; release 12.1.1.1) and sequence in T1-3D-TFE (TR ¼ 18ms, TE ¼ 6.9ms, FLIP ANGLE ¼ 25^A, PIXEL SIZE¼1.31 x 1.34 x 1 mm) to evaluate hippocampal volumes (v.n. 2.51 + 0.13 cm3). The diagnosis of dementia was based on NINCS-ARDRA criteria. The endpoint of conversion to AD was considered the Clinical Dementia Rating (CDR) ¼1. Results: In the 1-year follow-up 5 aMCI patients converted to AD with an annual conversion rate of 27.7%. At T0 based on the mean TDI score 4 patients were normosmic (22.2%), 12 hyposmic (66.6%) and 2 anosmic (11.1%). 4 of 5 aMCI patients that developed AD had significant bilateral hippocampal volume loss (< 1.3 cm3) associated to threshold, discrimination and identification scores on the TDI lower than patients who didn’t develop AD. Based on hippocampal volume we found 14 (77.7%) aMCI patients with hippocampal atrophy (mean 1.33 cm3), 1 (5.5%) aMCI patient with hippocampal hypotrophy (mean 2.3 cm3) and 3 (16%) aMCI patients with normal hippocampal volume (mean 3.06 cm3). A statistical significant correlation was found between MCI and hippocampal volume loss (p < 0,05) and between TDI score and CDR score at T0 and T1 (p < 0,05). 8 aMCI patients (46%) showed olfactory deficit associated to hippocampal volume loss, 6 aMCI patients (34%) only hippocampal volume loss, 1 aMCI patient (3%) only olfactory deficit and 3 aMCI patients (17%) had normal olfactory function and hippocampal volume. Conclusions:We found significant odor threshold, discrimination and identification deficits together with neuropsychological and MRI hippocampal volume loss in aMCI patients who converted to AD. Our findings suggest the potential utility of olfactory test and MRI hippocampal volumes for early detection of AD.