Olfactory Bulb and Gyrus Rectus Volumes in Alzheimer’s Disease: Associations with Eating Disturbances

Background and Objectives: Olfactory dysfunction is an early non-cognitive feature of Alzheimer’s disease (AD). The volumetric behavior of olfactory and related frontal structures and their link to eating disturbances remains unclear; we therefore compared olfactory bulb (OB) and gyrus rectus (GR) volumes between patients with AD and controls and examined their relationship with eating disturbances and their diagnostic value. Materials and Methods: In this single-center, retrospective, case–control study, 135 patients with AD and 49 age-matched controls underwent 3-Tesla MRI. Right, left, and total OB and GR volumes were measured. Groups were compared using the Mann–Whitney U test; age- and sex-adjusted logistic regression and receiver operating characteristic (ROC) analyses were performed; and OB and GR volumes were compared according to eating disturbance status in patients with AD, with adjustment for age and sex. p-Values were corrected for multiple comparisons using the Benjamini–Hochberg false discovery rate procedure. Results: All OB and GR volumes were significantly lower in patients with AD compared to controls (all p < 0.001), with the total OB volume nearly half that of the controls. Among patients with AD, all OB volumes were significantly lower in those with eating disturbances (all p < 0.001) and remained independently associated after adjustment for age and sex, whereas none of the GR volumes was significantly associated with eating disturbance status after adjustment. In adjusted models, every volumetric measure was independently associated with AD (all p < 0.001). The total OB volume showed the best diagnostic performance (AUC 0.940; sensitivity 0.82; specificity 0.98), while GR volumes performed less well (AUC 0.78–0.84). Conclusions: AD is associated with marked OB and GR atrophy. OB volume was associated with eating disturbances and discriminated AD from controls with high accuracy, supporting OB volumetry as an accessible candidate imaging marker that warrants prospective validation.