Olfactory Dysfunction in Chronic Rhinosinusitis: Mechanisms, Diagnosis, and the Role of Endoscopic Sinus Surgery.

Chronic rhinosinusitis (CRS) constitutes a multicausal inflammatory disease of the nose and paranasal sinuses, often associated with olfactory dysfunction (OD), a symptom that significantly impacts patients' quality of life. OD in CRS was traditionally thought to be related to mechanical obstruction of the olfactory cleft, but is now considered to be multifactorial, involving conductive, inflammatory, and sensorineural mechanisms as well. Type-2 inflammatory response (high interleukins IL-4, IL-5, IL-13), eosinophilia, and increased IgE are involved in epithelial damage, impaired neurogenesis, and persistent olfactory loss, especially in chronic rhinosinusitis with nasal polyps (CRSwNP). In addition, peripheral chronic inflammation may also play a role in central neural remodeling, which may potentially affect olfactory function. Objective psychophysical testing is necessary to accurately assess olfactory function because self-reports may lack reliability. Management strategies aim at reducing inflammation and restoring sinonasal ventilation. First-line therapy with intranasal corticosteroids and short courses of systemic corticosteroids may be useful for symptomatic relief. Biologic agents directed against type-2 inflammation have demonstrated significant benefits in selected cases. Functional Endoscopic Sinus Surgery (FESS) plays an important role in the treatment of refractory CRS to restore the airflow and to improve the delivery of topical drugs. Olfactory outcomes following surgery, however, are variable and often incomplete, reflecting underlying inflammation and neuroepithelial damage. Disease recurrence, especially in type-2-driven CRS, affects long-term outcomes, underscoring the necessity to incorporate surgery in an individualized, endotype-informed treatment strategy.