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of asthma in patients with CRSsNP or CRSwNP appears to be lower in Asians than Caucasians. 172 In patients with CRS, the coexistence of asthma is associated with a higher incidence of CRSwNP (56%) than CRSsNP (36%). 185 Asthma is often underdiagnosed in CRS patients but is more common in patients who subsequently are diagnosed withCRS. 17,30,165,183,186 The “unified airway” concept suggest that treatment of 1 disease could potentially improve the coexisting con dition. The association of comorbid asthma with lower QoL, more atopy and increased risk of revision surgery in CRS is related to the clinical status (eg, exacerbation) of asthma. 187–191 Endoscopic sinus surgery for CRS in asth matic patients has been reported to improve multiple clini cal asthma parameters with improved overall asthma con trol, reduced frequency of asthma attacks and number of hospitalizations, and decreased use of oral and inhaled corticosteroids. 189–192 Early ESS in the disease continuum also helped patients with recalcitrant CRS to decrease the risk of developing asthma. 97 V.C Recurrent Acute Rhinosinusitis (RARS) Recurrent acute rhinosinusitis (RARS) is defined as 4 or more episodes of ARS (defined in section V.A) per year with distinct symptom-free periods between acute episodes. 1 During symptom free periods, patients typically have normal endoscopic or radiologic examinations. The threshold of 4 episodes in a year was selected to reduce the risk of misdiagnosing or over diagnosing RARS. 201 How ever, some literature has suggested that 5 episodes per year should be considered as a threshold to maximize the value of surgical intervention. 202,203 There is growing concern surrounding the over or misdiagnosis of RARS. Acute exacerbations character ized by symptoms are not necessarily associated with objective (endoscopic or radiologic) evidence of sinonasal inflammation. 204,205 Surgical appropriateness criteria for RARS suggest a diagnosis should include at least 4 episodes per year as well as objective evidence (endoscopic or radi ologic) of an acute exacerbation. 206 There are also con flicting reports on whether sinonasal anatomic variations Asthma as a CRS Comorbidity Aggregate Grade of Evidence: C (Level 3: 14 stud ies; level 4: 2 studies; Table V-4).

V.B.3 CRS: Unified Airway Concept and Comorbid Asthma CRS and asthma are both common manifestations of an inflammatory process within the contiguous upper and lower airway system. The prevalence of asthma is around 25% in patients with CRS compared to 5% in the gen eral population. 158 The etiology or pathogenic mechanisms underlying the development and progress of these 2 condi tions are not fully understood, since both CRS and asthma are highly heterogeneous with respect to genetic back ground, environmental factors and the specific host reac tion of the airway mucosa. However, it is well known that the upper and lower airways share continuous air way anatomy, cell and humoral immunity, and experi ence common stimulations and risk factors. 31 Moreover, eosinophilia and airway remodeling, 2 major histological hallmarks of both diseases, have been suggested as the same pathologic disease process. 159–162 Therefore, asthma and CRS are associated with one another in the concept of the unified airway. 163 Indeed, epidemiological and clinical evidence has con sistently revealed the coexistence of CRS and asthma. A number of studies have shown that CRS and asthma fre quently coexist in the same patient, 20,160,164 and comor bid asthma has been associated with atopy and increased severity in CRS than controls. 165–168 CRS patients with asthma require significantly more health care for CRS and more revision sinus procedures overall than patients without asthma. 158,169 Treatment of CRS, medical or surgi cal, benefits concomitant asthma. 170,171 In a recent Korean population-based survey, a history of asthma increased the risk of developing CRS up to 2.06-fold (95% CI, 2.00 2.13). 172 Another cross-sectional population-based study in Iran also showed that CRS was more frequent among the participants with asthma (57.3%, OR = 2.3; 95% CI, 2.1-2.5), and there was a significant association between CRS and current, early and late-onset of asthma ( p < 0.001; OR = 4.4, 3.2 and 6, respectively). 173 CRS has been postulated as a risk factor contributing to the development and severity of asthma. The presence of CRS is associated with more severe asthma symptoms, particularly cough and sputum, 174 and appears to increase the risk of exacerbations in asthmatic patients. 174,175 Aran dom sample survey study, with over 52,000 adults aged 18-75 years in 12 European countries, showed that asthma was found to be strongly coupled with CRS appropri ate symptoms (adjusted OR, 3.47; 95% CI, 3.20-3.76). 164 The reported incidence of asthma varies from 2% to 38% in patients with CRS, 165–167,169,176,177 2% to 66% in CRSwNP, 159,165–167,169,176–184 and up to 68% to 91% in refrac tory CRSwNP. 160,167 Among these reports, the prevalence