Nasal Cytology Is Useful for Evaluating and Monitoring the Therapeutic Response to Biologics in Chronic Rhinosinusitis with Nasal Polyposis

<b>Background/Objectives</b>: In recent years, the recognition that type 2 inflammation plays a leading role in CRSwNP has enabled the more tailored treatment of the disease through improved patient endotyping. We studied 45 patients with severe CRSwNP who were treated with dupilumab or mepolizumab. The aim was to evaluate the efficacy of these treatments on endoscopic, clinical and patient reported parameters, and to assess whether nasal cytology could be useful for identifying responsive patients and monitoring their response to biologic drugs. <b>Methods</b>: Follow-up visits were scheduled at baseline (T0), and at 3 (T3), 6 (T6), 12 (T12), and 24 months (T24). At each visit, patients underwent blood analysis, nasal endoscopy, and nasal scraping for cytology. They also completed the SNOT-22 questionnaire, a visual analog scale (VAS) for nasal obstruction and smell perception, and the Asthma Control Test (ACT) test in cases of concomitant asthma. <b>Results</b>: Biological therapy demonstrated broad efficacy in disease management, based on both clinical and cytological findings. The Nasal Polyp Score, SNOT-22 questionnaire, VAS scores for nasal obstruction and smell, and ACT score showed progressive improvement. Blood eosinophil counts and total IgE levels also decreased over time (T0 vs. T24: <i>p</i> = 0.008 and <i>p</i> < 0.001, respectively). At nasal cytology, a reduction in eosinophil cell count and in the mixed mast cell-eosinophil pattern during treatment with both biologics were observed (T0 vs. T24: <i>p</i> < 0.001). Positive effects were typically recorded within six months of treatment and were sustained after two years. <b>Conclusions</b>: Although the histological evaluation of infiltrated tissues remains the gold standard for assessing mucosal eosinophilia, nasal cytology appears to be a simpler, non-invasive, and repeatable method for evaluating local eosinophilia. Identifying endotypes and assessing the severity of inflammation are crucial for predicting the efficacy of different treatment options.