Olfactory dysfunction in frontotemporal dementia and psychiatric disorders: A systematic review

Area of Science:

• Neuroscience
• Psychiatry
• Clinical Neurology

Background:

• Frontotemporal dementia (FTD) diagnosis is challenging due to symptom overlap with psychiatric disorders like depression and schizophrenia.
• Olfactory dysfunction is a common early symptom in both FTD and psychiatric conditions, often preceding other clinical signs.
• Understanding smell dysfunction profiles may aid in differential diagnosis.

Purpose of the Study:

• To systematically review and analyze studies on olfactory function in FTD, depression, schizophrenia, and bipolar disorder.
• To identify distinct olfactory dysfunction profiles, specifically in odour identification and discrimination, across these conditions.
• To evaluate the utility of olfactory testing in differentiating FTD from psychiatric disorders.

Main Methods:

• Systematic review of 74 studies examining olfactory function (odour identification and discrimination) in FTD, depression, schizophrenia, and bipolar disorder.
• Comparative analysis of olfactory performance across patient groups.
• Focus on common smell assessment measures.

Main Results:

• Frontotemporal dementia patients exhibited severe odour identification deficits but intact odour discrimination.
• Schizophrenia patients showed impairments in both odour identification and discrimination.
• Depression patients displayed no significant olfactory impairments; bipolar disorder findings were mixed.
• Olfactory testing differentiated FTD from depression and schizophrenia, but not reliably from bipolar disorder.

Conclusions:

• Distinct olfactory dysfunction profiles, particularly in odour identification, can help distinguish frontotemporal dementia from depression and schizophrenia.
• Olfactory testing, specifically assessing odour identification and discrimination, offers a promising, non-invasive tool for improving differential diagnosis in neurodegenerative and psychiatric conditions.
• Further research is needed to clarify olfactory profiles in bipolar disorder for complete diagnostic differentiation.