Olfactory bulb volume changes across Alzheimer’s disease stages

Background: Olfactory dysfunction is commonly seen in Alzheimer’s disease (AD) and has been reported in many studies. In this study, we measured the olfactory bulb volume (OBV) and olfactory sulcus depth (OSD) by MRI to see if they can help in distinguishing between healthy controls and different stages of Alzheimer’s disease (AD). Methods: This retrospective cross-sectional study included 125 participants, divided according to clinical stage (Control, Mild AD, Moderate AD, and Severe AD). OBV and OSD were measured by MRI. Welchs ANOVA were used to compare the mean OBV and OSD between the groups. Multiple linear regression was performed to check the relationship of OBV with stage, age, and gender. ROC analysis was used to find the diagnostic cutoff values. Results: Mean OBV varied by stage: 81.2±19.2 mm³ (Controls), 89.1±26.9 mm³ (Mild AD, vs Controls p=0.12), 60.3±19.8 mm³ (Moderate AD, vs Controls p<0.001), and 42.4±17.3 mm³ (Severe AD, vs Controls p<0.001). OSD showed no significant differences (p>0.05). Regression analysis indicated a significant association between OBV and AD stage (B=-18.39 for AD vs. controls, p<0.001) and a positive association with age (B=0.844, p=0.008). ROC analysis for AD (EVRE 3-4 vs. EVRE 1-2) yielded an AUC of 0.706 (95% CI: 0.612–0.800, p=0.001), with a cut-off of 56.25 mm³ providing 96.7% sensitivity and 40.0% specificity. Conclusions: OBV was significantly lower in moderate and severe AD, which shows that it may have diagnostic value in later stages of the disease. However, there was no significant decrease in Mild AD, meaning it may not be useful for early screening. Long-term studies are needed for understand if OBV can predict the progression to AD.