Variations in olfactory function among bipolar disorder patients with different episodes and subtypes.

Area of Science:

• Neuroscience
• Psychiatry
• Sensory Biology

Background:

• Bipolar disorder (BD) diagnosis and management can be challenging due to symptom heterogeneity.
• Olfactory dysfunction is increasingly recognized in various psychiatric conditions, but its specific role in BD subtypes and states remains under-investigated.

Purpose of the Study:

• To investigate olfactory sensitivity (OS) and olfactory identification (OI) in patients with different bipolar disorder (BD) subtypes (BD I vs. BD II) and episodes (manic, depressive, euthymic).
• To explore the potential of olfactory function as a biomarker for early identification and differentiation of BD subtypes and states.

Main Methods:

• A cohort of 117 hospitalized BD patients and 47 healthy controls underwent olfactory testing using the Sniffin' Sticks test for OS and OI.
• BD patients were classified into BD I (n=86) and BD II (n=31) groups, and further categorized into depressive (n=36), manic (n=44), or euthymic (n=37) episodes.
• Psychometric assessments included the Hamilton Depression Rating Scale (HAMD) and Young Manic Rating Scale (YMRS).

Main Results:

• BD patients exhibited significantly lower OS and OI compared to healthy controls.
• Statistically significant differences in OS and OI were observed between BD I patients and controls, and in OS between BD I and BD II groups.
• OS differed significantly across depressive, manic, and euthymic BD groups, and between manic and euthymic states. OI correlated positively with YMRS scores in BD I, while OS negatively correlated with HAMD scores in BD II.

Conclusions:

• This study provides novel pairwise comparisons of olfactory function between BD I and BD II patients.
• Olfactory sensitivity (OS) shows promise as a biomarker for distinguishing BD subtypes and differentiating acute phases from the euthymic state in bipolar disorder.
• Further prospective research is recommended to validate these findings and explore clinical applications.