Introduction: Olfactory impairment is one of the cardinal symptoms of chronic rhinosinusitis with nasal polyps (CRSwNP). However, the effect of 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 evidence on the impact of medical, surgical, and biological treatment on olfactory outcomes in patients with CRSwNP.
Methods: This review was conducted by 2 reviewers according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. The quality of evidence of all the 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. These assessed sinonasal surgery (n=23), biologics (n=15), and conventional medical treatment (n=6). The methodological quality was moderate-to-high in most. Overall, significant improvements in the sense of smell were detected with all the interventions analyzed and measured using an objective tool, a subjective tool, or both. However, most studies used different outcome measures, thus hindering comparisons between interventions, and data on clinically relevant changes were missing.
Conclusion: Oral corticosteroids, biologics, and sinonasal surgery improve the olfactory impairment associated with CRSwNP. However, the heterogeneous nature of existing studies does not allow accurate comparisons.

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