[Sense of smell in allergic rhinitis]

Olfactory dysfunction is one of the major complaints in patients suffering from allergic rhinitis. Little is known about the onset of hyposmia in seasonal allergy.

We performed two prospective studies to examine olfactory function in allergic rhinitis using an established (modified CCCRC) test for olfactory threshold, identification and discrimination.

In a pilot study the time-course of olfactory function in 14 patients with allergic rhinitis to grass pollen was examined at the beginning of the season. Olfactory function was evaluated birhinal on day 3, 7, 14, and 21 of the season. Preseasonally, all patients were normosmic. There was a significant decrease in threshold and identification between the third and fourteenth day of the season, resulting in a moderate hyposmia in the mean. Hyposmia was not correlated to subjective symptom of nasal blockage. Therefore, a follow-up study was performed on 17 patients and a control group with a similar study design including measurements of nasal volume flow (rhinomanometry) and an inflammatory cell activation marker (ECP) in nasal secretions. The time-course of the olfactory changes was much better correlated to the inflammatory measure than to nasal volume flow.

Patients with allergic rhinitis develop a significant olfactory dysfunction under allergen exposition. Inflammatory dysfunction of the olfactory epithelium seems to be more important than respiratory dysfunction in the pathomechanism of allergic hyposmia.