Introduction

Based on epidemiologic data, the prevalence of chronic rhinosinusitis (CRS) is estimated at 10.9% in Europe, 11.9% in the United States, 8% in China, and 5.5% in Brazil.1 CRS is a complex, multifactorial inflammatory disease of the nasal mucosa and paranasal sinuses. Its diagnosis is based on the criteria laid down in the 2020 European Position Paper on Rhinosinusitis (EPOS).2 According to these criteria, CRS is divided into primary and secondary, or localized and diffused, based on its anatomic distribution. Primary CRS may be related to type 2 (T2) inflammation or other types of inflammatory response. Depending on the profile of the cytokines produced, the subpopulation of CD4+ T lymphocytes (T helper [Th] cells) can be divided into 3 main effector groups protecting against various types of microbial infections (Th1, Th2, or Th17). The fourth subpopulation are follicular helper lymphocytes (Tfh), which activate type B lymphocytes in peripheral lymphatic organs.3 T2 immune response involves interleukin (IL)-C2, as well as type 2 cytotoxic T cells [Tc2] and Th2 cells. The latter 2 are responsible for the production of IL-4, IL-5, IL-13 (affecting the production of immunoglobulin E [IgE]), activation of macrophages through an alternative pathway, and activation of eosinophils. This type of immune response is triggered by parasitic infections, induces IgE-mediated allergic diseases, causes hyperplasia of the mucosal glands, and participates in chronic diseases involving eosinophilia.4,5

T3 immune response to bacterial and fungal infections is characterized by production of IL-17 and IL-22 by Tc17 and Th17 cells. Tfh lymphocytes are involved in the regulation of B-cell responses and antibody production. The main cytokine produced by these cells is IL-21.3

In Caucasians and some Asians, CRS with nasal polyps (CRSwNP) is characterized by predominance of T2 inflammation. IL-4 regulates the expression of vascular cell adhesion molecule 1, increasing the adhesion of eosinophils to the vascular endothelium. Eotaxins (IL-5 and IL-13) mediate eosinophil penetration into tissues.6 Local IgE production increases not only in response to airborne allergens, but also to Staphylococcus aureus enterotoxins, which are superantigens stimulating local overproduction of these antibodies. Activation of IgE-coated mast cells in the nasal mucosa and sinuses leads to their degranulation and stimulates further infiltration of eosinophils.7

Eosinophils express receptors for cytokines, chemokines, and adhesion molecules, which makes them a part of inflammatory response and homeostasis regulation. Thanks to the presence of receptors for bacterial patterns and the receptor for the Fc molecule, eosinophils can participate in the innate and adaptive responses. In response to stimuli, eosinophils release eosinophil cationic protein, major basic protein (MBP), eosinophil peroxidase, eosinophil-derived neurotoxin (EDN), cytokines, cytosolic Charcot–Leyden crystal protein / galectin 10 (CLC/Gal-10), and eosinophil extracellular traps.8 In vitro, MBP activates basophils, mast cells, and neutrophils, whereas EDN activates dendritic cells and CLC/Gal-10, promoting the T2 response.8 Chronic, primary, diffuse, T2-dependent rhinosinusitis with polyps often coexists with other eosinophilic diseases, such as asthma, IgE-mediated allergy, or hypersensitivity to nonsteroidal anti-inflammatory drugs (NSAIDs).2

Type 2 CRSwNP is a chronic disease of unclear etiology, requiring repeated endoscopic surgery and systemic steroid therapy. The recurrence of polyps and related symptoms are not the result of poorly performed surgery or incorrect conservative treatment; rather, they are caused by intensification of inflammatory processes at the molecular level. Treatment with monoclonal antibodies directed against IL-4 (particularly its receptor α subunit) or IL-5/IL-5 receptor can reduce eosinophilic inflammation, which allows for extending the time between surgical interventions and improves patient quality of life. Blood eosinophil count is an easily accessible biomarker of the disease severity, and has been listed among the criteria for scheduling a CRSwNP patient for biologic treatment.

We aimed to establish whether absolute blood eosinophilia could be a reliable criterion for scheduling CRSwNP patients for biologic treatment. Thus, we assessed the blood eosinophil count in patients with CRSwNP scheduled for endoscopic surgery of the nasal cavity. Patients with CRS without nasal polyps (CRSsNP) served as a control group. We also aimed to evaluate the relationship between the eosinophil count and 1) the extent of inflammation in the sinuses assessed with the Lund-Mackay (L-M) score, 2) number of procedures related to the presence of polyps, and 3) coexistence of other T2 diseases, such as allergy, NSAID hypersensitivity, and asthma.

Patients and method

This single-center, retrospective, observational, case-control study included patients treated at the Department of Laryngology and Laryngological Oncology of the Upper Silesian Medical Centre in Katowice between 2021 and 2022. The patients admitted to the Department for Endoscopic Surgery. Data on the CRS phenotypes, comorbidities (eg, IgE-mediated inhalant allergy, NSAID hypersensitivity, and asthma), and absolute blood eosinophilia were retrospectively analyzed. Information regarding previous surgical procedures involving the nasal cavity and sinuses was obtained from the patients’ records and medical history.

A diagnosis of IgE-mediated inhalant allergy was confirmed by a skin test or the presence of IgE antibodies specific to seasonal (tree, grass, weed) and / or perennial allergens (mites and mould spores, cat and dog allergens), evaluated on an outpatient basis. Pharmacologic treatment was introduced by an allergist. Patients with allergic reactions induced by other immune mechanisms (non–IgE-dependent allergies) were not included in this study.

NSAID hypersensitivity was confirmed based on medical history, that is, clinical signs involving the mucous membranes of the respiratory and digestive systems and / or the skin induced by 1 or more NSAIDs.9 Asthma was diagnosed and treated on an outpatient basis according to the Global Initiative for Asthma recommendations.10 Severity of the inflammatory lesions was assessed with the L-M score based on a sinus computed tomography scan. The degree of opacity in the maxillary, anterior, and posterior ethmoid, frontal, and sphenoid sinuses, as well as the ostiomeatal complex obstruction were assessed bilaterally on a scale from 0 to 2, with a maximum score of 24 points. All patients underwent endoscopic examination of the nasal cavity. The Meltzer Clinical Scoring System for nasal polyps was used to assess the polyp phenotype. This is a 0–4 point polyp grading system, with 0 points indicating no polyps; 1 point, polyps confined to the middle meatus; 2 points, multiple polyps of the middle meatus; 3 points, polyps extending beyond the middle meatus; and 4 points referring to polyps completely obstructing the nasal cavity.11

Absolute eosinophilia was assessed in each treated patient during routine blood tests using the Sysmex XN-1000 hematology analyzer (Sysmex, Warszawa, Poland).

The patients consented to the proposed routine procedures upon admission to the hospital. Due to a retrospective design of the study, approval of a bioethics committee was not required.

Statistical analysis

Patient baseline characteristics were summarized using descriptive statistics. The results were expressed as median values with interquartile ranges (IQRs) due to non-normal variable distribution. The nonparametric Mann–Whitney rank-sum test was used for comparisons between the 2 subgroups. The comparisons between frequencies were performed using the Z test for proportions. A linear regression model was constructed to determine the relationship of age, sex, presence of asthma, inhalant allergy, or NSAID hypersensitivity, and the L-M score with the peripheral blood eosinophil count in both groups. In the CRSwNP group, the number of previous functional endoscopic sinus surgeries (FESSs) was also included in the model. The cutoff value for eosinophils was determined based on receiver operating characteristic analysis and the Youden index. All analyses were performed with the STATISTICA 13.3 package (StatSoft, Kraków, Poland). P values below 0.05 were considered significant.

Results

Between January 1, 2021 and December 31, 2022, a total of 701 patients were treated for CRS, of which 407 (58.1%) were men. The median (IQR) age of the patients was 49 (38–62) years. The CRSwNP phenotype was diagnosed in 300 participants (42.8%) (Table 1). The patients with and without nasal polyps differed in several respects. In the CRSwNP group, there were more men, the patients were older, asthma and NSAID hypersensitivity were diagnosed more often, and inhalant allergy was less common. Also, the CRSwNP patients had more severe radiologic lesions in the sinuses, as reflected by a higher L-M score, and underwent more laryngological procedures (polypectomy and / or FESS). In this group, the absolute peripheral blood eosinophil count was higher (Table 1). In the entire group of patients, the cutoff value of the absolute blood eosinophil count for CRSwNP diagnosis was 150 cells/µl, for NSAID hypersensitivity it was 190 cells/µl, for asthma, 250 cells/µl, and for repeated sinus surgery, 250 cells/µl. The regression analysis showed that in the CRSwNP, group a greater absolute eosinophil count was observed in younger patients (β = –0.13; 95% CI, –0.25 to –0.02; P = 0.02), individuals with more severe sinus lesions according to the L-M score (β = 0.13; 95% CI, 0.01–0.25; P = 0.02), and those with asthma (β = 0.19; 95% CI, 0.06–0.32; P = 0.004). In the CRSsNP group, the eosinophil count was greater in the patients with more severe sinus lesions according to the L-M score (β = 0.3; 95% CI, 0.2–0.4; P <⁠0.001).

Table 1. Clinical characteristics of chronic rhinosinusitis patients with and without nasal polyps

Parameter

CRSwNP (n = 300)

CRSsNP (n = 401)

P value

Men

202 (67)

205 (51)

<⁠0.001

Age, y

54.5 (44–65)

45 (36–58)

<⁠0.001

Inhalant allergy

119 (39.7)

270 (60.3)

<⁠0.001

NSAID hypersensitivity

54 (18)

9 (2.2)

<⁠0.001

Asthma

121 (40.3)

37 (9.2)

<⁠0.001

Peripheral blood eosinophil count, cells/µl

250 (160–380)

135 (75–240)

<⁠0.001

Number of endoscopic surgeries

0

1 (0.3)

5 (1.2)

–

1

137 (45.7)

329 (82)

<⁠0.001

2

84 (28)

55 (13.7)

<⁠0.001

>2

78 (26)

12 (3)

<⁠0.001

Number of FESSs

0

1 (0.3)

7 (1.7)

–

1

194 (64.7)

340 (84.8)

<⁠0.001

2

75 (25)

47 (11.7)

<⁠0.001

>2

30 (10)

7 (1.7)

<⁠0.001

L-M score

16 (14–20)

9 (6–12)

<⁠0.001

Data are shown as number (percentage) of patients or median (interquartile range).

Groups were compared with the Z test for proportions or the Mann–Whitney rank-sum test.

Abbreviations: CRSsNP, chronic rhinosinusitis without nasal polyps; CRSwNP, chronic rhinosinusitis with nasal polyps; FESS, functional endoscopic sinus surgery; L-M, Lund-Mackay score; NSAID, nonsteroidal anti-inflammatory drug

Discussion

In this study, we assessed the eosinophil count in 2 main phenotypes of CRS in relation to the coexisting diseases, such as asthma, atopy, and NSAID hypersensitivity, and with regard to the intensity of sinus inflammation and the number of previous sinus procedures. We found that a greater absolute blood eosinophil count was associated with more advanced inflammatory process, as reflected by the L-M score, regardless of the CRS phenotype. However, in the CRSwNP group, a significantly greater eosinophil count was documented in younger patients with concomitant asthma and a higher L-M score. Our results are concordant with the findings of Bachert et al,12 who revealed that in the CRSwNP patients with a greater baseline eosinophil count (≥300 cells/μl), concomitant asthma and NSAID hypersensitivity were more frequent than in the patients with a lower baseline eosinophil count (≥150 cells/μl). The patients with higher baseline eosinophilia had a lower risk of reoperation or systemic steroid use during biologic treatment, as compared with the individuals with a lower baseline eosinophil count.

Taking into account the qualification criteria for biologic treatment, based on the 2020 EPOS guidelines,2 the European Forum for Allergy and Airway Diseases (EUFOREA) guidelines,13 the POLINA 2.0 consensus,14 and the SYNAPSE phase III study12 on CRSwNP patients, as well as our observations, absolute eosinophilia seems to be of equal or even greater importance than the number of previous sinus procedures or the use of systemic steroid therapy. Presence of asthma, a criterion listed in the EPOS and EUFOREA guidelines,2,13 was reflected by the eosinophilia level in our study group.

CRSwNP is considered severe when it affects patient quality of life, which can be assessed with the Sino-Nasal Outcome Test (SNOT-22) or using the visual analogue scale (VAS). On the other hand, uncontrolled CRSwNP is evidenced by restricted nasal patency, mucopurulent discharge, facial pain, impairment or loss of smell, sleep disorders, and fatigue, requiring long-term administration of antibiotics or systemic steroids.15 Within the polyp phenotype, endotypes with concomitant asthma and NSAID-exacerbated respiratory disease are particularly difficult to treat. In these endotypes, there are no doubts about the type of inflammation taking place in the mucous membranes of the respiratory tract. In the cases without concomitant asthma, the type of inflammation should be confirmed by evaluating at least 1 biomarker. It can be absolute blood eosinophilia, tissue eosinophilia (eg, tested using a cytologic smear from the nasal mucosa), or the total IgE level in atopic patients. In the EPOS and EUFOREA guidelines, cutoff values for ​​eosinophilia are 250 cells/μl or above and 150 cells/μl or above, respectively. According to the Polish Society of Otolaryngologists – Head and Neck Surgeons and the Polish Society of Allergology, biologic treatment should be considered when at least 3 of the following criteria are fulfilled: presence of T2-dependent disease, poor disease control, VAS score greater than or equal to 5 or SNOT-22 greater than or equal to 40, and concomitant asthma or atopic dermatitis. The required cutoff value of blood eosinophilia is 150 cells/µl or above.16

In our study, in the CRSwNP group, the median peripheral blood eosinophil count was 250 cells/µl, which indicates that 75% of the patients with this disease phenotype would meet the EUFOREA criteria, and 50% would meet the EPOS criteria. Therefore, it seems that a diagnosis of CRSwNP with the eosinophil count greater than or equal to 250 cells/µl would confirm the T2-dependent endotype of rhinosinusitis and, in combination with additional criteria, would facilitate the referral of patients for biologic treatment. Moreover, the same cutoff values of absolute blood eosinophil count were shown for asthma and repeated sinus surgery, and lower values were shown to predict the presence of nasal polyps and NSAID hypersensitivity. These data support the above suggestion that patients with an absolute blood eosinophil count of 250 cells/µl or greater may suffer from bronchial asthma or may have undergone previous sinus surgery, and thus may be candidates for biologic treatment, if they have nasal polyps.

Knowing the mechanism of inflammation occurring in the mucous membrane of the nasal cavity and sinuses, we can use new therapies to manage CRSwNP. Dupilumab and mepolizumab are currently registered in Poland for the treatment of CRSwNP. Dupilumab is a recombinant human IgG4 monoclonal antibody that inhibits IL-4 signaling via the type I receptor (IL-4Rα/γc) and both IL-4 and IL-13 signaling via the type II receptor (IL-4Rα/IL-13Rα). As a consequence, recruitment and activation of eosinophils are inhibited.17,18 Mepolizumab is a monoclonal antibody of the IgG1 κ class, directed against IL-5, thereby inhibiting IL-5 signaling and reducing the production and survival of eosinophils. The SYNAPSE study12 showed that the baseline number of eosinophils greater than or equal to 150 or greater than or equal to 300 cells/μl may be a useful biomarker of response to mepolizumab treatment in patients with severe CRSwNP.12 High baseline blood eosinophil values may be a risk factor for development of transient hypereosinophilia in patients treated with dupilumab, and requires monitoring of the eosinophil level during treatment.18 Results of the VENTURE study19 involving patients with asthma suggest that other factors, such as systemic steroid therapy, may interfere with the regulation of the blood eosinophil level, which should also be taken into account in the case of CRSwNP patients with high baseline eosinophil counts. However, it should be kept in mind that values greater than or equal to 1500 cells/μl require extended diagnostics toward hypereosinophilic syndrome or eosinophilic granulomatosis with polyangiitis.20

The results of our study indicate a relationship between the absolute number of blood eosinophils and the intensity of inflammation in paranasal sinuses. Blood eosinophil counts were greater in the CRSwNP patients with higher L-M scores and concomitant asthma. In the patients with CRSsNP, the blood eosinophil count was related only to the L-M score.

Blood absolute eosinophilia in CRSwNP patients is an important biomarker that may be used in qualification for biologic treatment.