Rhinitis: allergic or not?

Abstract

Until now, no consensus exists for the classification, definition and diagnosis of rhinitis. Very common symptoms include discharge, itching, sneezing, congestion and pain. Rhinitis-afflicted patients are consequently classified according to the suspected aetiology into allergic and nonallergic rhinitis. In this issue of Clinical Experimental Allergy, Ng et al. [1] describe preliminary critera for the definition of allergic rhinitis. This study may help to better characterise allergic rhinitis, since so far there is a clear lack of recognized diagnostic criteria. Rhinitis is one of the more frequent and widespread respiratory diseases, affecting about 25% of the population [2]. Rhinitis has been less investigated than asthma, perhaps because this nasal disease is rarely life threatening. Among humans, nasal breathing is vital only during early infancy. Later in life, breathing through the mouth only is tolerable, although it may interfere with sleep, working and social life. It can also lead to infections. The importance of nasal functions [3] explains the unfavourable consequences observed in rhinitis. The filtering function of the nose prevents penetration of many noxious particles into the lower airways. The heating and humidification of inhaled air through the nose avoids complications such as infections. Finally, olfaction is not only important for social life and the pleasure of good food, but also for recognising irritants [4]. All these functions can be altered in rhinitis, independently of the pathophysiology of the disease. Rhinitis is the most common form of allergic disease and diagnosis is usually established using clinical history, skin prick tests and specific IgE [5]. When the diagnosis is uncertain, challenges with allergens may be performed. Peak nasal inspiratory flow and rhinomanometry are long established methods to evaluate nasal provocation tests with allergens [6]. Acoustic rhinometry, based on sound-reflection analysis is more recent and provides a close estimate of nasal anatomy and congestion. This method is as sensitive and specific as peak nasal inspiratory flow in its evaluation of the allergic response to allergen provocation [7]. Nasal wash fluid is used to perform measurements of inflammatory mediators, including cytokines and other biochemical markers following an allergen challenge [8]. In common practice, nasal cytology is sometimes recommended to differentiate infectious from allergic rhinitis [9]. In case of bacterial infection staining of nasal brushing reveals neutrophils, and the presence of eosinophils suggests an allergic disease, less frequently nasal polyposis or the nonallergic rhinitis with eosinophilia syndrome (NARES). The degree of nasal eosinophilia has been correlated with the severity of allergic rhinitis and the mucous response to topical steroids. Nasal cytology is also useful in evaluating viral infections because viruses induce destructive changes of ciliated epithelial cells (ciliocytophoria). With all these methods at hand, it is uncommon that the diagnosis of allergic rhinitis cannot be established for a specific patient. However, the estimation of the prevalence of allergic rhinitis in various population groups remains difficult to assess, since most of the above mentioned diagnostic-approaches are time consuming and invasive. Ng et al. report in this issue [1] a scoring testing that was applied to distinguish allergic rhinitis patients from normal subjects. These authors have examined the relevance of clinical tests and laboratory measurements reported to be frequently associated with allergic rhinitis. The scoring testing was based on the derived δ-values (strength of association) for symptoms/signs, skin prick tests, total IgE and specific IgE. The three groups of additive scores that showed the greatest difference between allergic rhinitis and control subjects were symptoms/signs alone, followed by symptoms/signs + total IgE + skin prick tests and symptoms/signs + total IgE + specific IgE. There was no significant association between allergic rhinitis and skin prick tests + specific IgE, demonstrating the great importance of the clinical history of the patient: many people who are atopic by skin tests or specific IgE do not have symptoms of an allergic disease. Moreover, the δ-value of total IgE was much lower than that of skin prick tests and specific IgE. This result was foreseeable, because raised total IgE are encountered in only 50% of adults with allergic rhinitis. Moreover, age, familial environment, smoking and prevalent helminthic infections in certain regions induce great variations of total IgE levels [10]. Finally, there is a difference between the presence of specific IgE to common inhalant allergens and that of raised total IgE, which can correspond to a polyclonal IgE synthesis, as seen in nasal polyposis [11]. These observations are well illustrated in two recent epidemiological studies by Annesi-Maesano [12] and Tschopp [13], which have emphasised the importance of patient history and of skin prick tests. These authors concluded that total IgE was not a good criterion, because of the large overlap between allergic and nonallergic rhinitis. Moreover, the serum assays used to measure IgE may sometimes be inadequate for evaluating the role of IgE in allergic diseases: in humans, IgE may be produced locally such in the mucosa (as in the rat) and transported to the lumen under the control of IL-4 to be eliminated [14]. In such a situation, IgE should be measured in the mucosal fluids rather than in the serum. In summary, the diagnosis of allergic rhinitis should be based on a scoring testing, at least including a clinical history of the patient and allergic skin tests. Lastly, Ng et al. have limited their observations to patients with allergic rhinitis and normal subjects. Whether their criteria should be used to diagnose allergic vs chronic rhinitis has not been addressed. However, this information would be important. Allergic diseases are increasing in prevalence and appeared to be more commonly associated with western style of life [15]. Multiple factors may contribute to their augmentation, such as genetic factors, environment, infections [16], exposition to irritants, nutrition and immunisation status [171819]. It is thus of the utmost importance to establish a sensitive and specific methodology to easily categorise allergic vs. nonallergic rhinitis, with the idea to better identify risk factors for allergy development [20].