Allergic rhinitis (AR) is an upper airway disease that's caused by an IgE-mediated inflammatory reaction after allergen exposure (1), and it could contribute to decreased social activity, a poor quality of school life and decreased productivity in moderate-to-severe symptomatic patients (2-4). Its incidence is 10-25% worldwide and it is on the increase (5) as industrialization progresses. Thus, advanced treatment modalities are required and a more feasible classification system is needed for this propose.

AR had been classified as seasonal, perennial or occupational AR according to the exposed allergens (6). However, the previous classification had some limitations in that it is common that both seasonal and perennial allergens are sensitized and seasonal allergens cause perennial allergic symptoms or even perennial allergens cause allergic symptoms seasonally (7, 8)

The Allergic rhinitis and its impact on asthma (ARIA) group proposed a new classification based on the duration and severity of symptoms. AR is classified into the mild or moderate-severe groups according to the severity of symptoms and AR is also classified into the intermittent or persistent groups according to the duration of symptoms. Thus, AR is divided into four groups: the mild intermittent, mild persistent, moderate-severe intermittent and moderate-severe persistent groups.

In an epidemiological study in a Western country, within the total AR population, 29% of the patients had persistent AR and they had more severe symptoms than the intermittent AR patients (9). In another study in Italy, 1,321 AR patients were enrolled, and mild intermittent AR was diagnosed in 7.7% of the patients, moderate-severe intermittent in 17.1%, mild persistent in 11.6% and moderate-severe persistent in 63.6% (10). Comparison between the ARIA classification and the classical one was performed in France. About 43.7% of the patients who were classified as seasonal did in fact have persistent rhinitis, whereas 44.6% of the patients who were classified as perennial had intermittent rhinitis (11). A retrospective study in 9 Asian countries showed that intermittent rhinitis was observed in less than 20% of patients, whereas patients with persistent rhinitis comprised approximately 80% of the total patients. Although 25-30% of AR patients had mild allergic rhinitis, 60-70% had moderate-severe rhinitis (12).

Most of the previously reported studies included content about the prevalence of the ARIA classification or the difference of the ARIA classification from the classical one. There have been a few studies about the serum total IgE level, peripheral blood eosinophils and olfactory dysfunction in each ARIA group. Twenty one percent of AR patients showed abnormal olfaction in one study, and "blockers" were known to have a significant loss of smell in another study. But there have not been any reports about the distribution of patients with olfactory dysfunction in each of the ARIA groups.

In Korea, the patients with AR are still more commonly managed based on the previous classification rather than on the ARIA classification. In addition, there have been few studies using the ARIA guidelines for Asians. Thus, the objective of this study is to classify the patients using the ARIA guidelines and to compare nasal symptoms, coexisting diseases, olfactory symptoms, the serum total IgE and the blood eosinophil count among the ARIA groups.

The most common group according to the ARIA classification was moderate-severe persistent in this study, which is similar to the previous studies that reported on Westerners (14). In the European study for ARIA classification, the most common group was the moderate-severe persistent group (51.2%), followed by the moderate-severe intermittent group (41.8%), the mild intermittent group (3.9%) and the mild persistent group (3.1%) (15). There was no statistically significant relationship between the previous seasonal/perennial classification according to the time of exposure and the ARIA classification.

House dust mites were predominantly the most common allergen in all the groups. House dust mites accounted for almost 90% of the sensitized allergens. The data shows many patients were sensitized to multiple allergens because the sum of the proportion of allergens reached nearly 200% in each group. In other words, the seasonal or perennial AR patients were simultaneously sensitized to seasonal and perennial allergens. For this reason, the previous classification according to the time of exposure does not properly represent each group of AR patients (9, 16). Therefore, it is reasonable to group AR patients according to the symptom duration and severity based on the ARIA guideline.

Although the ARIA classification have been applied and investigated all over the world, there have been few studies on the laboratory differences among the 4 ARIA groups. Our study shows that there was a statistically significant difference between the groups for the peripheral blood eosinophil count (P=0.004). Blood eosinophils were more abundant in the 2 persistent groups than in the 2 intermittent groups. Interestingly, the eosinophil count did not show any difference between the mild and moderate-severe AR groups. In other words, the eosinophil count may reflect the symptom duration of AR rather than the symptom severity. On the contrary, although the serum total IgE was increased, it was not significantly different among the groups.

With regard to the AR-related symptoms, the difference of olfactory dysfunction among the 4 ARIA groups has not been reported on, although olfactory disorder caused by AR is one of the main concerns for otorhinolaryngologists. Olfactory loss can be caused by both conductive and sensorineural mechanisms. Long standing allergic inflammation as well as immediate allergic reaction can induce mucosal hypertrophy and swelling, resulting in blocking of the passage for odorants to be delivered from the atmosphere into the olfactory neuroepithelium. Olfactory receptor neurons can be irreversibly damaged by inflammatory mediators or oxidative free radicals, which may be released by allergic inflammatory cells. Reduction of the olfactory receptor neurons and displacement of the olfactory neuroepithelium by respiratory epithelium culminate in sensorineural loss of olfaction. Olfactory dysfunction was the most common in the moderate-severe persistent group and it was least common in the mild intermittent group. This finding may reflect that AR-induced olfactory loss is related with both the symptom duration and severity. The sensorineural loss of olfaction might be more related with the moderate-severe persistent group than with any other group, which could explain the more frequent loss of smell in that group.

This study is the largest study to analyze the ARIA classification of Korean AR patients. The study showed the moderate-severe persistent group is the most prevalent, the same as for Westerners. House dust mites were more prevalently sensitized allergens in Koreans than in Westerners. The laboratory tests demonstrated that the blood eosinophil count may be related with AR symptom duration, while the serum total IgE does not play a different role in 4 ARIA groups. The highest prevalence of olfactory disturbance in the moderate-severe persistent group was one of the most characteristic findings of this study. The ARIA classification might be more related with AR symptoms, the prevalence of asthma, olfactory loss and the laboratory tests results than the previous classification, and so the ARIA classification should be clinically applied to all the patients. Further, it should be investigated for determining the proper therapeutic approaches depending on this classification system.