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Objective: The purpose of this study was to assess olfactory function and olfactory bulb volume in patients with major depressive disorder (MDD) in comparison to normal subjects.
Method: Twenty treatment-free premenopausal, 25-45 year-old women diagnosed with long-term, severe MDD at the ?i?li Etfal Research and Teaching Hospital psychiatric outpatient clinics and 20 healthy women matched by age, education, smoking behavior, and frequency of upper respiratory tract infection participated in this study. Odor threshold, discrimination, and identification functions were assessed by Sniffin' sticks. Olfactory bulb volumes were calculated by manual segmentation of acquired T2-weighted coronal slices according to a standardized protocol.
Results: When OB volumes of patients and controls were analyzed with a two-way Analysis of Covariance, with age and education as the covariate and group as a factor, the patients had significantly larger OBs than the controls (right p=0.011; left p<0.001; largest p=0.008). Education has a significant effect as a covariate in the OB volume X group analysis. Significant correlations between OB volumes in relation to olfactory function were observed in the control group; however, there was no correlation between OB volume and olfactory functions in the patient group.
Conclusion: Our results showed that OB volume gets larger in long-term MDD. According to our study and former knowledge it is possible that during MDD, the hippocampus, amygdala, and OB differ in terms of activity and volume to compensate for each other and stabilize the patient's mood.