Introduction: Olfactory impairment is one of the cardinal symptoms of chronic rhinosinusitis with nasal polyps (CRSwNP), yet the effect of the currently available therapeutic options on the recovery of the sense of smell is not well defined. The aim of this systematic review was to compile the evidence on the impact of medical, surgical, and biological therapies on the olfactory outcomes in patients with CRSwNP.
Methods: This review was conducted by two reviewers, according to the Preferred Reporting Items for Systematic Reviews and meta-Analyses (PRISMA) guidelines. The quality of evidence of all studies included in the qualitative synthesis was evaluated using the Critical Appraisal Skills Programme (CASP).
Results: Forty-four studies were included in the qualitative synthesis (assessing sinonasal surgery [n = 23], biologics [n =15], and conventional medical treatment [n = 6]); most had moderate-to-high methodological quality. Overall, significant improvements in the sense of smell were detected with all analyzed interventions measured by either an objective or a subjective tool (or both). However, most studies used different outcome measurements, hindering comparisons between interventions, and data on clinically relevant changes were missing.
Conclusion: Oral corticosteroids, biologics and sinonasal surgery improve olfactory impairment associated with CRSwNP, but the high variability among existing studies does not allow accurate comparisons. 

Key words: CRSwNP, Olfaction, Impairment, Biologics, Surgery, Corticosteroids