1. Introduction

Chronic rhinosinusitis (CRS) is a common disease with significant impact on the patients’ health and the societal economy 1,2. Chronic rhinosinusitis is generally categorized into two major subtypes based upon phenotypic appearance: CRS without nasal polyps (CRSsNP) and CRS with nasal polyps (CRSwNP). Nasal polyps (NP) are benign inflammatory masses in the mucosa of the nose and paranasal sinuses1–3. CRSwNP is associated with morbidity and decreased quality of life 4.
CRSwNP is estimated to affect 1–4% of the general population and 25–30% of patients with CRS (Stevens, Schleimer and Kern, 2016; Fokkens et al., 2020). Yet, there is a paucity of prevalence data on CRSwNP across many geographic areas 2,5,6. Based on a few studies, the NP prevalence estimates in the Nordic countries range from 2.7% in Sweden to 4.3% in Finland, based on single municipality studies 7,8. Subsequently, updated population-based data on the prevalence and incidence of CRSwNP is required.
Epidemiological, clinical, and pathophysiological studies suggest that asthma is strongly associated with CRSwNP 9,10. Inflammation in the nasal mucosa and lower airways are directly related, with a correlation between the inflammatory profiles of nasal and bronchial biopsies in patients with CRSwNP 11. It has been reported that up to 45% of CRSwNP patients have or will develop asthma 9,12. The prevalence of CRSwNP is higher in patients with asthma (7%) compared to the general population (4%)13. However, in the Finnish asthma population, the prevalence of NP has been shown to be as high as 16.5%7.
The mainstay therapy of CRSwNP includes medical treatments such as nasal or oral corticosteroids. For patients with CRSwNP who do not respond to conservative therapy, endoscopic sinus surgery (ESS) is considered. CRSwNP patients have been demonstrated to benefit from ESS, although a part of the CRSwNP patients have polyp regrowth and a need for a revision ESS as signs of uncontrolled disease 14–17. Among Finnish patients treated with functional endoscopic sinus surgery (FESS), the prevalence of CRSwNP as the primary diagnosis has been reported to be 17% 18.
A limited number of studies indicate that both medical interventions and FESS improve nasal outcomes in patients with CRS and asthma,19,20 but, more information is needed about the burden of CRS and how it is affected by concomitant asthma. The aim of this nation-wide real-world study was to evaluate prevalence and incidence of CRSwNP in Finland, and to describe treatment burden of CRSwNP and how this is related to the presence and severity of co-morbid asthma.