Non-allergic rhinitis in children: Epidemiological aspects, pathological features, diagnostic methodology and clinical management.

Chronic rhinitis is a very common disease, as the prevalence in the general population resulted to be 40%. Allergic rhinitis has been considered to be the most frequent form of chronic rhinitis, as non-allergic rhinitis has been estimated to account for 25%. However, several evidences suggested that non-allergic rhinitis have been underrated, especially in children. In pediatrics, the diagnostic definition of non-allergic rhinitis has been often limited to the exclusion of an allergic sensitization. Actually, local allergic rhinitis has been often misdiagnosed as well as mixed rhinitis has not been recognized in most cases. Nasal cytology is a diagnostic procedure being suitable for routine clinical practice with children and could be a very useful tool to characterize and diagnose non-allergic rhinitis, providing important clues for epidemiological analysis and clinical management.

Core tip: This manuscript aims at describing the current evidences regarding non-allergic rhinitis in children, whose diagnosis is probably underrated. Here, we described the epidemiology and the diagnostic definition of non-allergic rhinitis, highlighting also the differences compared to allergic rhinitis. Moreover, pathophysiological aspects, the emerging evidences on local allergic rhinitis and the growing role of nasal cytology in the diagnostic work-up of pediatric chronic rhinitis are discussed. Finally, insights on the therapeutic approach are provided.

INTRODUCTION

Rhinitis is a general term indicating any inflammatory disease of the nasal mucosa. Clinically, rhinitis is defined by the onset of two or more of the following symptoms: Nasal discharge, sneezing, nasal itching and congestion. According to the duration of nasal symptoms, rhinitis is defined as acute (resolving within 10 d) or chronic (lasting longer than 10 d). Whereas acute rhinitis is usually a viral (more often) and/or bacterial illness, isolate chronic rhinitis (CR) (without sinusitis) does not recognize infectious agents as a common etiology. Actually, the superimposition of bacterial or - less frequently - fungal infections has been more often described in the clinical setting of chronic rhino-sinusitis (CRS); however, this topic goes over the aim of this review[1].

Although the most defined group of CR, both in adults and children, is represented by allergic rhinitis (AR), actually those often recognize also other causes, that are attributable neither to allergic factors nor to infectious agents. Such a large portion of CR that cannot be definitively linked to allergy (and to infections) was included in a very heterogeneous “basket”, named as non-allergic rhinitis (NAR): Here, several pathological entities have been enclosed and, indeed, NAR have been indicated with a number of terms (vasomotor, occupational, hormonal, atrophic, iatrogenic, idiopathic), according to the dominant clinical and/or pathologic aspects[2,3]. Thus, it is quite evident that NAR is still a very poorly defined medical entity, where several and different causes and mechanisms are supposed and, as a consequence, it has been often misdiagnosed and/or underrated, especially in the pediatric population[4].

Nowadays, the current definition of NAR merely relies upon the exclusion of an allergic and IgE-mediated mechanism, defining AR. Unfortunately, such a simplistic clinical distinction was complicated by the fact that AR and some forms of NAR share several clinical and pathologic features and, moreover, some patients present aspects that can be consistent with both allergic and non-allergic mechanisms, namely a “mixed” rhinitis[5].

EPIDEMIOLOGY

CR is a very common disease with an increasing incidence, especially in the Western countries, where the actual prevalence in the general population is between 10% and 40%, according to different studies. Despite such an epidemiological burden, CR have been considered mild disorders and that poor consideration contributed to underestimate such a diagnosis and, as a consequence, the real prevalence for long time. Actually, a lot of studies focused on AR, representing the most diagnosed type of CR, and showed that nasal symptoms often interfere with daily activities and alter the sleep pattern, leading to negative consequences on the social life and intellectual performances. All these aspects make CR be a global health issue characterized with significant direct and indirect costs for the society[6,7].

In general, an allergic etiology, namely AR, can be established only in around half adult cases of CR, which indicates that a significant portion of the problem is represented by NAR. Prevalence studies on adults estimated that NAR could affect almost 20 million people in the United States, 50 million people in Europe and more than 200 million people worldwide[6,8].

However, because of its poor clinical and pathological definition, NAR is often under-considered by clinicians and, as a consequence, the epidemiological burden is also under-estimated, especially in the pediatric age. Actually, the exact prevalence of NAR in children is not known, but the comparative prevalence between NAR and AR was estimated to be to be at least 1:3-4[4,9]. A recent retrospective analysis by Topal et al[10] regarding 472 consecutive children evaluated for CR within 1-year period, showed that 76.9% patients were diagnosed with AR and, thus, the remaining 23.1% children had NAR. Previously, another pediatric study by Chiang et al[11] enrolling 660 children (aged 1 to 18 year) with CR, provided very similar results, as AR was diagnosed in 75.9% cases and, by exclusion, NAR represented 24.1% of the total.

DEFINITION AND DIAGNOSIS OF AR

AR is caused by the immunologic sensitization to one or more environmental allergens, leading to the production of specific IgE that trigger some inflammatory events responsible for the nasal symptoms. Depending upon the individual sensitization(s), AR can show different temporal patterns of symptoms, but the classical distinction between seasonal and perennial has been completed by the classification of the project Allergic Rhinitis and its Impact on Asthma (ARIA). It considers both the duration and the severity of nasal symptoms. The temporal patterns of AR have been defined by the following definitions: (1) episodic rhinitis, when nasal symptoms are very limited, as those occur if the allergic individual comes in contact with an allergen exposure that is not a part of the daily environment (e.g., a cat at a friend’s house); (2) intermittent rhinitis, if symptoms last fewer than 4 d every week or fewer than 4 wk/year; and (3) persistent rhinitis, if symptoms are present for more than 4 d a week and last more than 4 wk/year. The severity of the nasal disease is considered as being moderate to severe, if one or more of the following clinical items are reported, respectively: (1) abnormal sleep; (2) impairment of daily activities, sport and leisure; (3) difficulties at school and/or work; and (4) troublesome symptoms. If no one of these clinical aspects is present, AR is defined as being mild[12,13].

Although no existing study extensively described the disease-specific pattern of recurrence, duration of symptoms and impact on the quality of life of pediatric NAR, this classification could be suitable anyway and all these aspects must be evaluated in every child complaining of CR, as those are fundamental to achieve a correct diagnosis of AR or NAR. Indeed, the evidence of one or more positive results of skin prick tests and/or serum allergen specific IgE that, by itself, indicates only the allergic sensitization, must be placed into the specific clinical picture, in order to be interpreted correctly and to support a final diagnosis of AR. The diagnosis of AR to one or more environmental allergens can be safely established only if the profile of allergic sensitization(s) displayed by the individual is consistent with the temporal pattern, the persistence and the severity of nasal symptoms[12,14]. Conversely, it is not correct to reach a diagnosis to AR if nasal symptoms and the related temporal pattern, frequency and severity have not resulted to be linked to allergen exposure, although skin prick tests and/or serum of allergen specific IgE are positive for that allergen. In this case, CR is supposed not to be allergic, namely NAR, or to have more pathological components, both allergic and non-allergic, namely mixed rhinitis or overlapped rhinitis, as discussed forward. In conclusion, the nasal anatomy must be always considered too in the diagnostic pathway of CR, as anomalies of turbinates and septum can contribute to the nasal disease; moreover, adenoid hypertrophy must be investigated in children. Finally, the occurrence of superimposed chronic rhinosinusitis (CRS) should be actively excluded in the setting of AR with atypical symptoms and/or whenever the clinical disease and the pattern of environmental sensitization seem to be mismatching[15].

NAR

Currently, NAR is basically diagnosed by exclusion of AR in the appropriate clinical setting. NAR is a chronic condition of the nasal mucosa showing symptoms of nasal congestion and rhinorrhea with no evidence of allergic sensitization through skin prick tests (SPT) and dosage of serum specific IgE for environmental allergens[16].

According to such a definition, it is estimated that at least a quarter of patients complaining of CR have NAR, but they might be more numerous, considering that some have mixed rhinitis and that NAR are still underrated[17]. According to data from United States National Rhinitis Classification Task Force, which were collected more than 15 years ago, around 17 millions of Americans were affected with NAR and as many people suffered with a combination of non-allergic and allergic nasal disease (mixed rhinitis). As a percentage, AR, NAR and mixed rhinitis affected 43%, 23% and 34% of patients, respectively. Moreover, it was evident that NAR and mixed rhinitis occurred more frequently in adults than in children, were more common in female patients and used to have a perennial rather than seasonal course[18,19]. These observations have been replicated by many other studies and the prevalence of NAR ranged between 17% to more than 50%[20-22].

Although NAR were considered to be more prevalent in adults, actually those could represent a significant burden in the pediatric age, too. Unfortunately, detailed information regarding the prevalence and burden of NAR in children is lacking: That may partially be explained by the few allergen challenges that are performed in young ages[21]. Moreover, the term NAR does not indicate a specific clinical entity and, therefore, includes a number of different forms of CR: As a consequence, several classifications and terminologies generated further imprecisions in the epidemiological evaluations. Indeed, the classification of NAR still relies upon the presence of comorbidities and/or the evidence of triggering factors and/or some pathological features. Unfortunately, most cases of NAR have not been associated to any of the aforementioned conditions and, thus, have been defined as being idiopathic and/or vasomotor[3].

According to the Global Atlas of Allergic Rhinitis and Chronic Rhinosinusitis edited by the European Association of Allergy and Clinical Immunology (EAACI)[23], the following forms of NAR have been recognized: (1) non-allergic rhinitis with eosinophilia syndrome (NARES); (2) hormonal rhinitis (pregnancy, associated to menstrual cycle, acromegaly, hypothyroidism); (3) rhinitis of the elderly; (4) gustatory rhinitis (hot and spicy foods, alcohol consumption, etc.); (5) atrophic rhinitis (primary or secondary to sinus surgery, autoimmune and/or immune-mediated diseases); (6) cold-air induced rhinitis (triggered by cold and/or windy climate conditions); (7) drug-induced rhinitis (nasal decongestant “rhinitis medicamentosa”), aspirin, systemic alpha- and beta-adrenergic antagonist, phosphodiesterase inhibitors, calcium channel blockers, neuroleptics, etc.); (8) occupational non-allergic rhinitis (irritants, corrosive substances); and (9) idiopathic rhinitis (“vasomotor rhinitis”).

The NAR consensus panel of World Allergy Organization (WAO) edited a similar classification, excluding automatically both anatomical/mechanical nose abnormalities and CRS. Moreover, systemic medical conditions (endocrine/metabolic, autoimmune and miscellanea) leading to NAR symptoms have been considered separately. Thus, eight subtypes of NAR have been classified: (1) drug-induced rhinitis; (2) gustatory rhinitis; (3) hormonal-induced rhinitis (including responses to endogenous female hormones, basically the rhinitis of pregnancy); (4) non-allergic rhinitis with eosinophilia; (5) senile rhinitis; (6) atrophic rhinitis; (7) cerebral spinal fluid leak; and (8) non-allergic rhinopathy (corresponding to vasomotor rhinitis and those forms related to climate conditions)[24].

Taking in account what stated above, it is evident that a systematic classification of NAR based upon pathological mechanisms is still distant (Table 1). Therefore, rather than trying to find some correspondences of the aforementioned categories of NAR in the pediatric population, it seems to be more useful to discuss some specific aspects of NAR, such as the emerging evidence on local allergic rhinitis (LAR), the growing interest on nasal cytology for the possibility of defining the features of NAR inflammation and the pathogenic role of some noxious agents for the nose, such as environmental pollutants.

Table 1

Classifications of non-allergic rhinitis by World Allergy Organization and European Academy of Allergy and Clinical Immunology[23,24]

WAO	EAACI
Drug-induced rhinitis	Drug-induced rhinitis
Local a-adrenergic agonists (“rhinitis medicamentosa”: Excessive use of nasal decongestants); systemic a- and b-antagonists; aspirin; phosphodiesterase (PDE) V inhibitors; ACE inhibitors; calcium channel blockers; antipsychotics
Gustatory rhinitis	Gustatory rhinitis
Anterior rhinorrhea and/or post-nasal drip after eating, especially hot or spicy foods
Hormonal-induced rhinitis	Hormonal rhinitis
Rhinitis of pregnancy and menstrual cycle-associated rhinitis
NARES	NARES
Presence of eosinophilia in the nasal secretions
Occupational rhinitis	Occupational non-allergic rhinitis
Irritant-induced rhinitis and corrosive rhinitis
Senile rhinitis	Rhinitis of the elderly
Persistent watery rhinorrhea without any identifiable trigger
Atrophic rhinitis	Atrophic rhinitis
Primary or secondary (extensive surgery, chronic granulomatous disorders, other)
Non-allergic rhinopathy	Idiopathic rhinitis
Nasal congestion and/or rhinorrhea triggered by irritants and/or weather changes, but also chronic without identifiable triggers
Cerebral spinal fluid leak	Cold air-induced rhinitis
Persistent rhinorrhea after cranio-facial trauma or facial/sinus surgery	Rhinorrhea and/or nasal congestion and/or burning triggered by cold and/or windy condition

NARES: Non-allergic rhinitis with eosinophilia syndrome; WAO: World Allergy Organization; EAACI: European academy of allergy and clinical immunology.

LAR

LAR is a type of CR showing the same phenotypic characteristics as AR, actually without any remarkable positivity of environmental skin-prick tests (SPT) and/or serum specific IgE. In specific studies, LAR is characterized by an allergen-related nasal hyper-reactivity, despite the absence of specific systemic atopy, as could be evidenced through specific nasal provocation tests (NPT), performed by administering intra-nasally a set of purified airborne allergens. In this clinical setting, the positive response to specific NPT suggested the presence LAR, which could be confirmed by recovering also allergen-specific IgE in the nasal mucosa[25,26]. Indeed, LAR and AR have been demonstrated to have similar patterns of inflammation, sustained by Th2 polarized immune responses: Probably, different initiating immunological events and mechanisms converging to a final common pathway of nasal inflammation may exist[27,28].

The local production of IgE in the nasal mucosa has been largely demonstrated in patients with AR, where the allergen exposure directly drives the antibody class switch recombination[29,30]. The presence of IgE specific to house dust mite in the nasal mucosa of patients with CR displaying negative SPT, but positive specific NPT, was reported in 1975 by Huggins et al[31]. Starting from 2000, Carney and Powe published a series of studies investigating nasal allergy due to the local production of IgE, defined as “entopy”. They were able to demonstrate the presence of mast cells, eosinophils and IgE+ cells in a selection of archival samples of nasal mucosa from patients affected with idiopathic CR: In addition to an increased number of mast cells, some showed a positive staining for IgE specific to grass pollen[32]. Eventually, Rondón et al[33] and Wise et al[34] described a cohort of NAR patients manifesting positive response to specific NPT to house dust mite: That result was reported in around 50% cases and, interestingly, specific IgE were detected in the nasal lavage of more than 10% of those.

Poor SPT technique and/or quality of allergen preparations or a cover allergy, namely the sensitivity to not tested allergens, have been suggested to explain some cases of apparent entopy. Additional pathological mechanisms, such as non-IgE mediated hypersensitivity and other tissue-specific immune responses could be considered in patients showing specific nasal hyper-reactivity, but not local IgE[35].

Epidemiologically, LAR might affect more than 40% people diagnosed with NAR. In a study including 428 patients with CR, Rondón et al[36] diagnosed AR, LAR and NAR in 63%, 26% and 11% of patients, respectively. Importantly, in addition to highlighting the epidemiological importance of LAR among CR, this study noticed that 36% of patients with LAR had rhinitis since childhood. Moreover, some authors suggested that LAR might be the first step of the natural history of AR, especially in polysensitized and young patients[37]. Indeed, some studies showed that children could develop systemic atopy to grass pollen only in the second or third season of nasal symptoms[38]. However, such a hypothesis upon LAR as an initial stage of AR needs to be tested adequately and immune processes might differ according to allergens. So far, the most prevalent allergen sensitizations identified in patients with LAR have been house dust mite, grass and olive pollen, but other allergens, including molds, animal dander and occupational substances, have not been completely investigated yet and might have a role[39,40].

However, that LAR is not only an adult disease and can arise from the pediatric age was evident also in the large follow-up study by Rondón et al[41,42] : Indeed, at least 35% of patients diagnosed with LAR and followed-up were 14-20 years old, confirming that the diagnosis should be considered in children too. Actually, this study showed also that the rate of conversion of LAR to “systemic” AR, namely displaying positive SPT and/or serum specific IgE, was only 6.8% and was similar to the percentage observed in healthy controls. Thus, these observations seemed to support the concept that LAR and AR could be different pathological entities. The first pediatric study assessing specific nasal hyper-reactivity and mucosal IgE was carried out by Fuiano et al[43] who analyzed 192 children aged 3-15 years and showing at least one positive SPT for aeroallergens (among house dust mite, grass pollen, olive pollen, Parietaria and Alternaria): Of those, 67.6% were symptomatic and 34.6% were asymptomatic. Between these two groups, a striking difference in nasal IgE was found, being 77% vs 13%, respectively. This study suggested a major role of nasal IgE in determining symptoms in children sensitized to environmental allergen, but also highlighted the presence of other mechanisms than or in addition to the production mucosal IgE, being able to suppress its activity (in asymptomatic children positive for nasal IgE) or to replace it (in symptomatic children negative for nasal IgE)[44]. The same authors replicated similar analysis in children suffering from CR during the period when Alternaria spores can be present in the environment. Interestingly, they found that most children (64.3%) had negative SPT for Alternaria, but were positive for nasal specific IgE; only 16.1% were positive to both tests and the remaining 19.6% had a positive SPT without nasal IgE. These results represented the first pediatric evidence that an allergic sensitization manifesting with CR can be mediated by an exclusive production of specific IgE in the nasal mucosa. Unfortunately, current evidences on pediatric LAR are insufficient to draw any consistent conclusion, as appropriate prospective studies are still lacking[45].

PATHOPHYSIOLOGICAL ASPECTS

According to the findings of studies including nasal cytology, AR can display different forms and severity of inflammation related to the allergic sensitization and, possibly, the season. Similarly, NAR can be classified according to several inflammatory patterns. These observations supported the concept that several immune-pathological mechanisms could be involved in both AR and NAR. Moreover, nasal cytology also demonstrated that AR and NAR coexist in some patients, leading to so-called overlapped rhinitis: Thus, more mechanisms seem to interplay or, perhaps, some of those could be shared between AR and NAR[46]. Importantly, some studies showed synergistic interactions in the inflammatory nasal responses between the specific IgE-mediated component of AR and the superimposition of non-specific irritation induced by environmental pollutants (e.g., diesel exhaust particulate, ozone, etc.), maybe in a bidirectional way[5].

By definition, AR and LAR are sustained by an IgE-mediated inflammation and are mainly associated to a Th2 immune response. However, among seasonal and perennial forms of AR, nasal cytology evidenced different features of the inflammatory infiltrate into the nasal mucosa, which suggested some substantial differences in the pathophysiological immune cascade anyway. On the contrary, by exclusion, NAR included all that is not promoted by an IgE-mediated pathogenesis. A series of non IgE-mediate immune responses are plausible, considering the heterogeneity of NAR, as evidenced by the nasal cytology and by the clinical observation. Unfortunately, most pathophysiological aspects of NAR have not been unveiled yet. Moreover, in addition to immune-mediated mechanisms, several evidences showed that some neurogenic responses seem to play a fundamental role in the development of NAR inflammation and, probably, are involved in AR, too[47-49].

Non IgE-mediated immune mechanisms could take place in several classified forms of NAR. In occupational rhinitis, lymphocytic infiltrates have been described, in association to epithelial desquamation and glandular hypertrophy. In atrophic rhinitis, different inflammation patterns can be seen, including granulomatous lesions. Conversely, inflammatory changes are less evident in other forms of NAR: For instance, in gustatory rhinitis, rhinitis medicamentosa or idiopathic (vasomotor) rhinitis, the nasal symptoms mainly resulted from the increased glandular secretion and the mucosal edema due to a local transudate, rather than from the presence of exudate and abundant inflammatory cells. Indeed, some authors preferred to refer these forms as rhinopathy, rather than rhinitis[3,24,50].

Therefore, in addition to pure immunologic mechanisms, actually a complex series of neuroendocrine pathways have been proposed to explain the pathophysiology of several forms of NAR and, in some extent, those could be involved in AR, too. Probably, both immune and neuroendocrine systems interact in the nasal mucosa of subjects suffering from CR, but those might have a different importance according to the type of NAR. Some evidences supported the involvement of autonomic neural responses in the pathophysiology of NAR. The neural regulation of upper airways relies upon sympathetic (adrenergic) and parasympathetic (cholinergic) fibers, which regulate the activity and the trophism of epithelial, vascular and glandular components of the nasal mucosa. Sympathetic neuromediators, being mainly norepinephrine and neuropeptide Y, cause local vascular constriction; however, in a lesser extent, those innervate also the glandular structures, decreasing the nasal secretions. Conversely, parasympathetic fibers, through the secretion of acetylcholine and some neuropeptides (particularly, vasoactive intestinal peptide), stimulate nasal glands and induce vasodilation. Actually, the neural system of the nasal mucosa includes also the sensory innervation supplying the septum, the lateral walls, the anterior parts of nasal floor and the inferior meatus. Among these nerves, non-adrenergic and non-cholinergic nervous fibers have been demonstrated in the human nasal mucosa. Predominantly, those resulted to be sensory unmyelinated C-fibers and have been demonstrated to be involved in the realization of several protective nasal responses (such as sneezing, mucus production and mucosal congestion) against potential noxious stimuli entering in the nasal cavities. The activation of these unmyelinated sensory C-fibers leads to the release of several neuropeptides [Substance P (SP), calcitonin gene related peptide (CGRP) and neurokinins] in the human nasal mucosa, through an antidromic conduction, in response to a large variety of stimuli[50,51].

Thus, this neurogenic reactivity seems to be dominant in those forms of NAR where the cellular inflammation resulted to be poorly expressed. However, some evidences suggested that the neural factors could play a role also in AR and in other forms of NAR anyway. Interestingly, a denser innervation of sensory C-fibers in the nasal mucosa was demonstrated in different forms of NAR, including idiopathic rhinitis, occupational rhinitis and some drug-induced rhinitis. Moreover, this hyper-innervation was associated to an increased expression of some neuropeptides (SP and CGRP, in particular) in the mucosal nerve fibers and, importantly, this finding was observed also in patients with AR, where some neuroinflammatory mechanisms might worsen the clinical expression of AR and/or promote the occurrence of overlapped rhinitis. Indeed, further investigations might determine whether overlapped rhinitis could be part of a continuum between AR and NAR, where immunologic responses (both IgE-mediated and non IgE-mediated), inflammatory/irritant responses upon exposure to chemicals and/or particulate matter and neurogenic factors develop over the time starting from an initial trigger[52-54]. In fact, non specific nasal hyper-reactivity, being an abnormal or excessive reaction of the nasal tissue (in term of glandular activity, mucosal inflammation and vascular leakage) after the exposure to a non allergenic stimulus that is usually innocuous to most people, has been demonstrated in patients with both NAR and AR. Such a nasal hyper-reactivity seemed to result mainly from the impaired balance of the activity of the aforementioned neural local reflexes. Indeed, several inflammatory mediators have been demonstrated to interact with sensory nerve endings in the nasal mucosa, which resulted to release several neurotrophins, in addition to the aforementioned neuropeptides. The formers would be responsible of the hyper-innervation seen in CR, both AR and NAR, whereas the latters would contribute to up-regulate the local inflammation by promoting the transcription of pro-inflammatory cytokines, in addition to eliciting the vascular and glandular responses causing nasal symptoms[55,56].

DIAGNOSIS OF NAR IN CHILDREN

Pediatric NAR is poorly defined. The available information is quite heterogeneous and most concepts have been derived from NAR in adults. Indeed, there are no pediatric studies recognizing the categories of NAR, as classified by EAACI or WAO, because those classifications were tailored for the adult population. By instance, hormonal, atrophic and occupational rhinitis are related to adult diseases or activities, as well as drugs involved in the occurrence of NAR are not used in the pediatric age and food causing gustatory rhinitis are not usually given to children. Therefore, the current diagnostic work-up of pediatric CR is often limited to the identification of AR, NAR (in general) and mixed rhinitis[4,21]. Such a diagnostic limitation is partially due to the fact that investigational techniques being useful to evaluate nasal obstruction (e.g., rhinomanometry) and nasal hyper-reactivity (e.g., nasal provocation test) cannot be applied to children so easily as to adult people, where those have been considered as important diagnostic tools, in order to define objectively the entity and the trigger factors of CR[57].

Rhinomanometry is a technique allowing an objective estimation of nasal airway obstruction and, therefore, should be also an essential part in the setting of nasal challenge procedures[58]. Whereas some nasal symptoms, like rhinorrhea and sneezing, are clinically evident, actually nasal blockage could be difficult to be assessed subjectively: The individual perception of nasal obstruction can be influenced by several factors and could mismatch with objective measurements of nasal patency. Indeed, available pediatric studies on the correlation between subjective scores and objective techniques for estimating nasal obstruction provided conflicting results[59,60]. Recently, a pediatric study including 284 children aged 6-14 years showed that a major part of children under-estimate or over-estimate their nasal obstruction and concluded that an objective measurement of nasal patency could improve the clinical management[61]. Here, children were evaluated by anterior active rhinomanometry that provides an accurate evaluation of nasal obstruction or resistance through the measurement of nasal airflow generated by a known pressure gradient[61,62]. An alternative technique is represented by acoustic rhinometry, which is basically based upon the amplitude and temporal analysis of the reflections of incident sound waves on the nasal cavities, calculating the cross-sectional area at different depths[63]. However, both techniques require considerable standardization to obtain reproducible results and experience to interpret the results. Actually, Peak Nasal Inspiratory Flow could represent a simple, reproducible and inexpensive technique, but it is effort dependent and, thus, could be difficult to be used in the pediatric population[57].

Another important tool in the differential diagnosis of NAR should be the nasal provocation test (NPT) and, ideally, the objective measurement of nasal obstruction should be used to assess the results, in addition to symptom scores. Specific NPT consists of triggering a nasal allergic response by administering a standardized allergenic extract locally in the nose. Non specific NPTs have been used to evidence non-allergenic nasal hyper-reactivity, namely an abnormal nasal reaction upon the exposure to several physical (e.g., cold air) or chemical (e.g., methacholine, mannitol, distilled water, etc.) agents being innocuous for most people. However, the use has been often limited to the research field and more studies are needed to evaluate the clinical usefulness and to standardize the methodology[56,58].

Specific NPT was primarily introduced in order to evaluate the clinical significance of a specific allergen sensitization in multi-sensitized patients. In the clinical setting of NAR, specific NPT could be useful to diagnose LAR, through the positive response to specific allergens in the setting of a CR without evidence of systemic atopy. Unfortunately, as discussed above, both techniques for estimating nasal patency objectively and NPT are difficult to be used in the routine allergy practice with children[64,65]. Indeed, the daily clinical experience in the pediatric allergy clinic includes children showing a clinical history consistent with AR in absence of positive findings of SPT and/or serum specific IgE. Here, the potential alternative to the complicated execution of NPT and/or rhinomanometry might be the detection of allergen specific IgE in the nasal mucosa[45]. Marcucci et al[66] described a method to detect nasal IgE in children, by placing into the nostril (in contact with the septum nasal mucosa) a paper strip whose surface had been covalently coupled with a specific allergen. Recently, Fuiano et al[44] recalled this method and carried out some pediatric studies by using nasal strips where a colorimetric reaction provided a semi-quantitative evaluation of the presence of specific nasal IgE. These authors sought nasal IgE specific to some aeroallergens (Alternaria, house dust mites, Grass Pollen, Olive pollen and Parietaria) in 192 children with positive SPT for one or more aeroallergens. A significant association between the presence of specific nasal IgE and nasal symptoms was observed in systemically sensitized children. Eventually, another study showed that measuring nasal IgE could be useful to unveil local allergic rhinitis to Alternaria and to avoid a misdiagnosis of NAR[66]. Alternatively, specific nasal IgE have been measured in the nasal secretions by immunoassay: Rondón et al[67] described a detection rate of specific nasal IgE to grass pollen of around 30%-35% in their cohort of LAR patients (defined by the positivity to specific NPT), which suggested a limited sensitivity of their method or perhaps the involvement of other immunologic mechanisms.

In summary, the testing of nasal specific IgE still needs to be improved and standardized and there are no available studies regarding the diagnosis of LAR in children through the evaluation of nasal IgE and/or specific NPT[45]. Recently, Gómez et al[68] proposed a role for basophil activation test (BAT) in the diagnosis of LAR: They found a sensitivity of around 50% in patients diagnosed with LAR to house dust mite, but that remains an isolated experience till now.

Thus, the diagnostic work-up of NAR in children is still limited to the exclusion of AR in most cases, as further diagnostic investigations cannot routinely performed in children (e.g., specific NPT, rhinomanometry, acoustic rhinometry) or showed no acceptable sensitivity and/or standardization (nasal specific IgE, BAT). However, a simple and inexpensive method to investigate patients (including children) with CR is represented by nasal cytology that might allow the description and classification of nasal diseases according to the inflammatory features. Moreover, a number of studies regarding nasal cytology have been performed also in the pediatric age and, therefore, a specific section will be dedicated.

NASAL CYTOLOGY

Nasal cytology consists of the microscopic analysis of surface cells of nasal mucosa. The suitable biological sample can be collected through a sterile swab or by scraping and is usually obtained by anterior rhinoscopy in order to reach the middle portion of the inferior turbinate. Thus, the material must be placed on a glass slide and, after it is fixed by air-drying, it can be stained according to May-Grunwald-Giemsa method. This simple staining allows identifying correctly all the normal cellular components of the nasal mucosa, the inflammatory cells and also bacteria and fungi, if those are present. Therefore, nasal cytology is endowed with several aspects allowing a routine use in allergy daily practice, including the pediatric setting: It is non-invasive, easy to perform, non-time-consuming and inexpensive[69].

The result of nasal cytology is the rhinocytogram that, in healthy controls, shows only ciliated cells and mucous-secreting cells of the pseudo-stratified epithelium of the nasal mucosa, in addition to sparse neutrophils. On the contrary, the presence of more abundant neutrophils and/or other inflammatory cells (eosinophils, mast cells, lymphocytes), as well as the presence of bacteria and fungi, represents a sign of nasal pathology. Nasal cyto-pathology has been studied in several nasal diseases and it might be a promising diagnostic tool for allergic and non-allergic rhinitis[70].

AR can be caused by several environmental allergens, differing as regards the immunological properties and the presence during the year. AR caused by indoor allergens, such as house dust mite, are usually perennial, as the patients complain of nasal symptoms all over the year and, accordingly, the rhinocytogram is characterized with a persistent infiltration of neutrophils and, in a lesser extent, of eosinophils, describing a pathological pattern of “minimal persistent inflammation”. Seasonal AR is often triggered when the pollens are present in the atmosphere and, therefore, the nasal symptoms are limited within a specific period of the year. In this setting, the rhinocytogram is very rich of all inflammatory cells, including neutrophils, lymphocytes, eosinophils and mast cells; by contrast, the cytological aspect of nasal mucosa can be completely normal outside the pollen season[71].

Interestingly, nasal cytology provided a heterogeneous landscape of NAR, both in adults and children, but EAACI and WAO classifications considered only non-allergic rhinitis with eosinophilia syndrome (NARES), as a separated cyto-pathological entity of NAR[3]. That should include those patients having the same clinical features as AR, but not positive SPT and/or serum specific IgE, namely LAR[72]. Under this limited perspective, all the other variants of NAR could be defined as non-NARES. Actually, nasal cytology suggested that the situation is more complex than two variants of NAR[73]; moreover, very recent evidences suggested that also NARES might recognize immunological mechanisms other than entopy[74]. Gelardi et al[73] described at least four cytological patterns of NAR (Figure 1): (1) NAR with eosinophils (NARES); (2) NAR with mast cells (NARMA); (3) NAR with neutrophils (NARNE); and (4) NAR with eosinophils and mast cells (NARESMA).

Figure 1

Nasal cytology of non-allergic rhinitis. A: NARES; B: NARMA; C: NARNE; D: NARESMA. NARES: Non-allergic rhinitis with eosinophilia syndrome; NARMA: NAR with mast cells; NARNE: NAR with neutrophils; NARESMA: NAR with eosinophils and mast cells.

These authors tried defining the incidence, the clinical aspects and the prognosis of these different cytological forms of “cell-mediated non-allergic rhinitis”. NARES and NARNE resulted to be the most abundant forms among children, as those were recognized in 46.5% and 40.6% cases, respectively. NARMA has been detected in 10.5% cases and NARESMA in the remaining 2.6%. On the contrary, in adulthood the relative proportions among all these forms of NAR seem to be more balanced and, particularly, NARESMA has been reported as affecting around 25%-30%, like NARES. Importantly, these two types resulted to be associated to the most severe clinical manifestations, such as non-allergic asthma, nasal polyposis and aspirin intolerance. Particularly, NARESMA was described as leading to the worst complications, including major respiratory disturbances (sleep-apnea and severe asthma). Significant respiratory symptoms and complications were almost absent in children with NARMA: Thus, the presence of eosinophils in the nasal mucosa resulted to be the most important determinant for the severity of the clinical disease. Despite the significant portion of NARES in the pediatric population, actually respiratory severe symptoms have not been seen as in adults, as those probably require a number of years of rhinopathy to develop. The other prevalent form of NAR in children resulted to be NARNE, as described above. NARNE was associated to cystic fibrosis, but it is supposed to have a multifactorial etiology and, particularly, it has been linked to the exposure to a number of irritants, including air pollution and cigarette smoke[73,75-77].

A large series of pollutants and chemicals have been reported to be involved in the etiopathogenesis of “environmental” NAR. Many of those have been related to occupational exposures (e.g., volatile organic compounds, paper dust, acetic acid, etc.), but others are common environmental pollutants[78]. A significant difference of inflammatory changes in the nasal cytology specimens was observed between people living in highly polluted urban areas and rural residents[79].

Environmental tobacco smoke, including sidestream or second-hand tobacco smoke exposure, has been demonstrated to have detrimental effect on several organs, especially in children. A wide variety of tobacco smoke effects have been described on the immune system and, of course, respiratory airways - and nose as first - are particularly exposed. Effects on immune cells functions and cytokines production have been reported in nasal mucosa and adenoidal tissue of children exposed to passive smoke[80]. Another important irritant for the respiratory system is ozone, whose concentration in the ground-level atmosphere increases in polluted areas. Experimental studies showed that ozone induces epithelial abnormalities and inflammatory responses of the nasal mucosa. A pediatric study reported a significant association between outdoor ozone concentration and levels of leukocytes in the nasal secretions[81]. Similarly, the particulate matter of the urban environment and, particularly, particles derived from diesel exhaust, have been described to increase the expression of inflammatory cells and molecules at several level of the respiratory system, including the nasal mucosa. Also fine particulate matter (PM ≤ 2.5 μm) was shown to increase significantly the percentage of eosinophils and several inflammatory mediators in the nasal lavage fluid of asthmatic children, but not in healthy children[82]. Thus, environmental pollution could exacerbate allergic inflammation and/or promote the development of new allergic sensitization at the respiratory level, especially in children, leading to mixed patterns of allergic and non allergic rhinitis in some cases[83,84].

Nasal cytology provided another important contribution under this perspective, as introduced the concept of mixed or “overlapped” rhinitis, namely the simultaneous presence of different forms of inflammatory rhinopathies in the same patient[85]. Particularly, there are patients (including children) diagnosed with AR, but that diagnosis actually is not fully consistent with the nasal symptoms and/or the related temporal pattern. In these cases, including both seasonal and perennial forms of AR, the superimposition of a form of NAR could be suspected and nasal cytology could provide fundamental clues. By instance, there are children suffering with a pollen-related AR who have nasal symptoms during the winter, when the rhinocytogram can show the presence of eosinophils, as well as there are children with house dust mite AR who have an abnormal clinical course and whose rhinocytogram can display mast cells and/or eosinophils, in addition to the pattern of minimal persistent inflammation (showing usually a preponderance of neutrophils). Those are typical examples of patients where an overlapped rhinitis should be suspected. Gelardi M and Landi M proposed some clinical and cytological criteria, in order to evaluate the likelihood of the presence of an overlapped rhinitis. Schematically, cytological features of overlapped rhinitis could be the finding of eosinophilia > 20% and/or mast cells > 10% in the rhinocytogram of patients with perennial CR and of patients with seasonal CR outside the pollen period corresponding to the personal allergic sensitization[78,86].

The possibility to unveil an overlapped rhinitis through nasal cytology might ameliorate the clinical and therapeutic management of these patients and also could have implications in the epidemiological analysis of pediatric CR and complications (e.g., asthma, nasal polyposis, chronic rhinosinusitis, etc.). Adult studies suggested that the presence of inflammation ad the type of inflammatory cells in NAR influences the clinical features and the risk of comorbidities[52,76].

Indeed, AR and NAR could be overlapping conditions in a greater number of cases than previously thought. Distinguishing isolated AR and overlapped rhinitis might improve the clinical management, as those recognize different clinical presentation, comorbidities and therapeutic responses. However, in order to achieve a better correlation between cyto-pathological patterns and clinical features of CR, a systematic application of nasal cytology and further studies are needed, both in adults and children. That might lead to a wider understanding of nasal pathophysiology, to a better classification of nasal diseases and, finally, to a rational therapeutic approach.

THERAPEUTIC MANAGEMENT

Once the diagnosis of AR has been established, the therapeutic approach includes the avoidance of allergen exposure, whether it is practicable, and the control and/or prevention of nasal symptoms by local or systemic anti-histamine drugs, intra-nasal steroids, leukotriene-receptor antagonists and, in a lesser extent, intra-nasal cromones and decongestants. Among those drugs, intra-nasal steroids have been demonstrated to be able to produce the greatest relief, as those mainly improve the nasal obstruction. Unfortunately, all these drugs control the symptoms, but cannot cure the allergic disease[87].

According to the “allergic/atopic march” hypothesis and to the “united airways disease” concept, AR can be associated to lung function test abnormalities and/or anticipate the onset of asthma. Thus, an important aim of the therapy of AR with identifiable allergenic triggers should be also prevention of the progression to asthma or other respiratory diseases, in addition to ameliorating patient’s life quality. Such a goal may be reached through the inclusion of specific immunotherapy (SIT) in the early treatment of AR. Indeed, SIT - unlike symptomatic drugs - has been demonstrated to modulate the immune mechanisms underlying the allergic disease and, therefore, it is the only treatment that currently could modify the natural history of allergic diseases[88]. SIT has been administered by two main ways: Subcutaneously (SCIT) or sublingually (SLIT). In many European countries, SCIT is still the most common way to administer allergy immunotherapy; however, SLIT has been gaining success, especially in the pediatric population, where it could be preferred because it is easily accepted and it is basically lacking of systemic and life-threatening adverse reactions[89,90]. Moreover, several systematic reviews supported the specific use of SLIT in the treatment of AR in children, as well as the EAACI position paper on pediatric rhinitis did. Recent analyses inferred a moderate strength and general evidence that SLIT improves pediatric AR and conjunctivitis, ameliorating symptoms and/or decreasing the drug consumption[12,91-93]. This evidence resulted to be stronger for grass pollen SLIT in the treatment of isolated AR, whereas the evidence for house dust mite SLIT effectiveness is still considered “of moderate-low quality”, as resulted from few available randomized controlled trials. Anyway, some indirect beneficial effects, as the prevention of asthma development and the reduction of respiratory infections, must be considered[94,95]. Moreover, as discussed previously, it must be reminded that the importance of a correct diagnostic definition of pediatric CR might affect these conclusions on the efficacy of SLIT. By instance, NAR sustained by the exposure to environmental pollutants producing similar nasal inflammatory changes and disease as house dust mite AR might could affect the outcome analysis of SLIT, by worsening the nasal inflammation due to allergy or by misleading the correct diagnosis. So far, very few studies faced this topic, but an interesting study showed that the exposure to passive smoke significantly reduced the clinical response to SLIT in children affected with AR due to house dust mite[96].

On the contrary, achieving a diagnosis of LAR in patients affected with NAR could have a major impact on the therapeutic management. Indeed, the cornerstone therapy of AR produced a good clinical response in patients with LAR and, particularly, those could receive further important benefit from SIT too. Rondón at al[97] reported a significant improvement of symptom and medication scores in 20 patients affected with LAR sensitized to grass pollen after receiving SCIT. However, so far there no pediatric studies regarding drug therapy and SIT in LAR.

As regards the treatment of NAR, the list of drugs basically includes most of molecules used in the management of AR. Unfortunately, patients with NAR resulted to be less responsive to the pharmacological therapy than patients affected with AR, in general[98].

Antihistamines have been largely used for the treatment of NAR. Compared to AR, non-sedating second generation molecules have not resulted to be so effective, whereas some benefits have been observed with first generation antihistamines, probably due to the greater anticholinergic activity. Actually, several studies supported the effectiveness of topical antihistamines in NAR, especially azelastine. Nasal spray containing azelastine have been approved for use in children aged six years and older, but there are no pediatric studies assessing its efficacy in children with NAR[98-100]. The association of azelastine with an intranasal corticosteroid, usually fluticasone propionate, resulted even more effective in the treatment of adult NAR. Similarly, that association was approved for use in children older than five years; however, the available studies on this drug included children aged 12 years and older, which suggested a similar efficacy in AR and NAR[101,102].

Thus, antihistamines and/or topical steroids are the mainstay of the general treatment of NAR. Additional drugs have been used with specific indications. By instance, topical anticholinergic medications, containing ipratropium bromide, could be recommended for patients having rhinorrhea as isolate or dominant nasal symptom, namely vasomotor rhinitis. Specific studies addressing the efficacy of ipratropium nasal spray in pediatric NAR are lacking; however, it has been studied in children complaining of rhinorrhea because of allergy or common cold and resulted to be easy to be administered, safe and effective also in children as young as 2 years[103,104]. In children saline nasal irrigation is considered the first step and the basic tool in every therapy for rhinitis and, indeed, resulted to be useful in the management of NAR, too. This procedure resulted to improve nasal symptoms, relieving post-nasal drip, nasal congestion and also sneezing. Nasal irrigation with isotonic saline irrigation seemed to ameliorate the mucociliary clearance, promoting the removal of allergens, biofilms and inflammatory mediators[6,105].

Finally, several adjunctive therapies have been proposed in adults, such as topical capsaicin, anti-leukotrienes and oral/intranasal decongestants. Unfortunately, there is no experience in the pediatric field at all[99,106]. However, some recommendations (based upon personal observations) have been reported in Table 2, according to the inflammatory pattern recovered by the nasal cytology.

Table 2

Recommendation for the treatment of pediatric non-allergic rhinitis, according to nasal cytology

	NARES	NARESMA	NARMA	NARNE
Topical anti-histamines	1	1	1	2
Systemic anti-histamines	1	1	1	2
Topical corticosteroids	1	1	1	1
Systemic corticosteroids	1	1	1	2
Ipratropium bromide	2	2	2	2
Anti-leukotrienes	1	1	1	2
Cromones	3	3	3	2
Nasal decongestant	3, 4	3, 4	3, 4	3, 4
Nasal saline irrigation	1	1	1	1

1: Recommended; 2: Not recommended; 3: Uncertain recommendation; 4: Permitted in children younger than 12 years, according to the dosage and for no more than 10-14 d. NARES: Non-allergic rhinitis with eosinophilia syndrome; NARMA: NAR with mast cells; NARNE: NAR with neutrophils; NARESMA: NAR with eosinophils and mast cells.

CONCLUSION

CR is a very common medical issue in children, as its incidence was estimated to be 40% in Western countries. Allergic rhinitis is considered to be the most frequent form of CR in children, whereas non-allergic rhinitis resulted to account for at least 25% of cases, according to few available pediatric studies. Actually, pediatric non-allergic rhinitis is poorly defined and is likely to be underrated. Indeed, although local allergic rhinitis is often misdiagnosed as being non allergic, a lot of CR do not receive the appropriate attention after an allergic cause has been excluded. Moreover, cases of non-allergic rhinitis could be lost because of a misdiagnosis of allergic rhinitis or because of its coexistence with allergic rhinitis, defined as mixed or overlapped rhinitis. Currently, the diagnostic definition of pediatric non-allergic rhinitis is often limited to the exclusion of allergy, as several investigations, such as nasal provocation tests and objective measurement of nasal patency, are not suitable for routine clinical practice with children. Actually, important clues could come through the growing application of nasal cytology in the diagnostic approach of children complaining of CR. That might lead to a better definition and classification of pediatric non-allergic rhinitis and, as a consequence, to an appropriate clinical management.