Olfactory dysfunction in chronic rhinosinusitis: insights into the underlying mechanisms and treatments

ABSTRACT

Introduction

Olfactory dysfunction (OD) is a typical symptom of chronic rhinosinusitis (CRS), which adversely affects the patient’s quality of life and results in mood depression. Studies investigating the impairment of olfactory epithelium (OE) have indicated that inflammation-induced cell damage and dysfunction in OE plays a vital role in the development of OD. Consequently, glucocorticoids and biologics are beneficial in the management of OD in CRS patients. However, the mechanisms underlying OE impairment in CRS patients have not been fully elucidated.

Areas covered

This review focuses on mechanisms underlying inflammation-induced cell impairment in OE of CRS patients. Additionally, the methods used for detection of olfaction and both currently available and potentially new clinical treatments for OD are reviewed.

Expert opinion

Chronic inflammation in OE impairs not only olfactory sensory neurons but also non-neuronal cells that are responsible for regeneration and support for neurons. The current treatment for OD in CRS is mainly aimed at attenuating and preventing inflammation. Strategies for use of combinations of these therapies may achieve greater efficacy in restoration of the damaged OE and consequently better management of OD.

KEYWORDS:

• Basal stem cells
• biomarkers
• chronic rhinosinusitis
• glucocorticosteroids
• olfactory dysfunction
• olfactory epithelium
• olfactory tests
• olfactory training

Article highlights

• The olfactory epithelium (OE) of CRS patients demonstrates structural abnormalities; including erosion, damaged physical barrier, squamous metaplasia, respiratory epithelium replacement, and inflammatory cell infiltration.

• In the OE of CRS patients, functions of both olfactory sensory neurons and non-neuronal cells are impaired by chronic inflammation. Changes in cell number, morphology, and function of different cell types are summarized.

• Current methods for detection of olfaction include subjective psychophysical tests, and objective olfactory event-related potentials and electro-olfactogram, which currently have low clinical application. In addition, biomarkers are being determined for displaying olfactory function.

• Medication, surgery, and olfactory training have some beneficial effects on the recovery of olfaction. Stem-cell-based therapy targeted to promote regeneration of the OE and differentiation of olfactory neurons is being investigated as a potentially novel and efficacious therapy for OD in CRS patients.

Declaration of interest

The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This work was supported by grants from national key R&D program of China (2022YFC2504100), national natural science foundation of China (82025010, 82171109), the program for the Changjiang scholars and innovative research team (IRT13082), Beijing municipal administration of hospitals’ Dengfeng/Youth plan (DFL20190202, QML20200202), and CAMS Innovation Fund for Medical Sciences (2019-I2M-5-022).