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Olfaction in allergic rhinitis: A systematic review

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Olfactory dysfunction is a key symptom in patients with allergic rhinitis (AR). Despite the implications for quality of life, relatively few articles have tested olfactory function in their investigations. The current systematic review aimed to investigate the following 2 questions: (1) What does AR do to human olfaction? (2) How effective is the treatment of AR in restoring the sense of smell? A comprehensive literature search was performed, and human studies of any design were included. A total of 420 articles were identified, and 36 articles were considered relevant. Data indicate that the frequency of olfactory dysfunction increases with the duration of the disorder, and most studies report a frequency in the range of 20% to 40%. Although olfactory dysfunction does not appear to be very severe in patients with AR, its presence seems to increase with the severity of the disease. There is very limited evidence that antihistamines improve olfactory function. In addition, there is limited evidence that topical steroids improve the sense of smell, especially in patients with seasonal AR. This is also the case for specific immunotherapy. However, many questions remain unanswered because randomized controlled trials are infrequent and only a few studies rely on quantitative measurement of olfactory function.

Section snippets

Methods

A comprehensive literature search was performed in August 2014 with the help of a professional librarian specialized in medical database reviews. All human studies published in English or German were included. The search strategy was adjusted to the database in use and was specified as follows (Medical subject heading [Mesh]/mh, title/abstract [tiab], title [ti], and abstract [ab]):

PubMed (no date restriction): (“Rhinitis, Allergic, Perennial” [Mesh] or “Rhinitis, Allergic, Seasonal” [Mesh] or

Search results

After eliminating duplicate findings, 420 articles were identified by using the search criteria described above. In the initial evaluation 74 articles were considered relevant for this review, leading to exclusion of 346 articles based on the title, abstract, and key words. After evaluation of the full-text version, 38 articles were additionally excluded. The 38 articles were excluded as follows. Seven articles were meeting abstracts,9, 10, 11, 12, 13, 14, 15 and 1 was published in French.16

Effect of AR on olfaction

Numerous studies indicate that olfaction is affected by inflammatory causes1, 2; see Doty and Mishra3 for a review. The frequency and severity of olfactory dysfunction in patients with AR were examined. In the present review the term olfactory dysfunction is used to describe a reduced sense of smell based on patient self-report or quantitative measures. The terms hyposmia and anosmia are restricted to corresponding results of quantitative tests. The most frequently used quantitative tests

Antiallergic therapy and its effect on olfaction

Various therapeutic approaches for the treatment of AR and related complaints have been investigated with regard to their effect on olfaction. However, studies primarily looking at the effect on olfaction are rare. Nevertheless, therapeutic approaches from studies investigating the effects on olfactory function are as follows: oral and topical antihistamines, topical steroids, surgery for the reduction of the inferior nasal turbinate in nasal obstruction caused by AR, specific immunotherapy,

Effect of AR on olfaction

Although olfactory dysfunction is a key symptom of AR, surprisingly few studies have investigated this symptom. Even fewer studies have measured olfactory function despite the availability of various reliable and valid olfactory tests (eg, UPSIT or the Sniffin' Sticks Test). The fact that patients with nasal dysfunction are known to mistake changes in airflow for changes in olfactory function (eg, Landis et al8) might question the reliability of qualitative measurements. Regardless of these

Conclusions

Olfactory dysfunction is frequently experienced by patients with AR and, in combination with decreased nasal patency, decreases quality of life. Frequency and severity increase with symptom severity and disease duration. Accordingly, olfactory dysfunction is more pronounced in patients with perennial/persistent AR than in those with seasonal AR.

Antiallergic and anti-inflammatory therapy both appear to be effective in patients with AR, at least as topical steroids, immunotherapy, and to a

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    Disclosure of potential conflict of interest: B. A. Stuck has received research support from MedaPharm GmbH. T. Hummel declares that he has no relevant conflicts of interest.

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