Olfactory markers for depression: Differences between bipolar and unipolar patients.

Area of Science:

• Neuroscience
• Psychiatry
• Sensory Science

Background:

• Olfactory dysfunction is increasingly recognized in mood disorders.
• Previous research suggests altered smell perception in depression, but comparisons between unipolar and bipolar depression across different mood states are limited.

Purpose of the Study:

• To compare olfactory function in unipolar and bipolar patients during depressed and euthymic states.
• To identify specific olfactory variations distinguishing these patient groups and mood states.
• To explore the potential of olfactory assessment as a diagnostic tool for mood disorders.

Main Methods:

• Recruited 176 participants across five groups: depressed bipolar (DB), euthymic bipolar (EB), depressed unipolar (DU), euthymic unipolar (EU), and healthy controls (HC).
• Assessed olfactory function using Sniffin' sticks threshold and identification tests.
• Evaluated odor pleasantness, intensity, familiarity, and emotion, alongside clinical dimensions of depression, mania, anxiety, and anhedonia.

Main Results:

• Smell identification was impaired in depressed unipolar (DU) patients compared to euthymic unipolar (EU) patients and controls.
• Lower hedonic ratings for pleasant odors were observed in DU and depressed bipolar (DB) patients compared to EU and euthymic bipolar (EB) patients, respectively.
• Hedonic ratings correlated negatively with social anhedonia in EB patients and with anxiety and anhedonia in EU patients.

Conclusions:

• Odor identification of pleasant odors is altered in both unipolar and bipolar depression.
• Unipolar patients may recover olfactory identification in remission, while bipolar patients retain deficits.
• Hedonic ratings of pleasant odors may differentiate unipolar and bipolar depression, suggesting olfactory assessment as a potential screening tool for mood disorders.