Correlation Between Olfactory Bulb Volume and Chronic Depression: A Magnetic Resonance Imaging Study

Objective: Olfactory dysfunction can be seen secondary to various diseases, such as sinonasal disease, infections of the upper respiratory tract, head trauma, and neurodegenerative diseases. A small number of recent studies have focused on olfactory dysfunction in different neuropsychiatric disorders. This study aimed to investigate olfactory bulb (OB) volume in patients with chronic major depression, as diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV). In particular, we investigated patients treated with selective serotonin reuptake inhibitors (SSRIs). To the best of our knowledge, this is the first study to investigate this subject. Methods: Participants included 31 outpatients (17 females and 14 males) with chronic major depression recruited from the University School of Medicine and Public Hospital psychiatry outpatient clinic between March 1 and August 31, 2013. Participants were examined using the Beck Depression Inventory (BDI). All patients were receiving treatment with a single SSRI. The BDI was also administered to a control group of 31 healthy volunteers (16 females, 15 males). All participants were recruited over the telephone after the study design was finalized. Additionally, both groups underwent a magnetic resonance imaging (MRI) scan with a 1.5-Tesla MRI system. Volumes of the right and left OBs were determined using MRI scans of the head and a standardised protocol for OB examination. Results: OB volumes were calculated separately for the depressed and the control groups. MRI measurements revealed significantly smaller olfactory bulb volume in patients with chronic major depression as compared to the control group. Furthermore, we detected a negative correlation between BDI score and olfactory bulb volume. Conclusions: Olfactory bulb volumes are notably smaller in patients with chronic major depression treated only with SSRIs (fluoxetine, sertraline, citalopram, escitalopram, paroxetine). To our knowledge, this is the first study to reveal reduced olfactory bulb volume in patients with chronic major depression. This study has demonstrated a negative correlation between OB volume and elevated depression scores.