Objective: To compare the efficacy of corticosteroid irrigation (CSI) and intranasal corticosteroid spray (INCS) in reducing polyp size, improving nasal symptoms, and assessing HPA-axis suppression in non-surgical patients with chronic rhinosinusitis with nasal polyps (CRSwNP).

Methods: Twenty-four patients from the Allergy and Rhinology Clinic, Songklanagarind Hospital, were randomized into: CSI + placebo spray (n = 13): Budesonide irrigation (0.5 mg/day) + saline spray. Placebo irrigation + INCS (n = 11): Saline irrigation + budesonide spray (512 mcg/day). Nasal symptoms were assessed using VAS-TNSS and SNOT-22. Polyp grading was evaluated via video nasal endoscopy using mLKS and Lildholdt's scale. Serum cortisol levels were measured at baseline, 4-12 weeks.

Results: After 12 weeks, the CSI + placebo spray group showed a significant reduction in mLKS scores (8.54 ± 1.94 vs. 4.82 ± 1.94; p < 0.001), with greater improvement than the placebo irrigation + INCS group (Δ4 (3, 4) vs. Δ1 (0, 2); p = 0.003). VAS-TNSS and SNOT-22 scores showed no significant differences. Serum cortisol levels remained normal.

Conclusion: Corticosteroid irrigation is more effective than nasal sprays in improving mLKS scores in non-surgical CRSwNP patients after 12 weeks, with no evidence of HPA-axis suppression.