Association Between Olfactory Function and Asthma in Adults

Abstract

Purpose: Chronic rhinosinusitis (CRS) and allergic rhinitis (AR) are common asthmaassociated upper airway diseases. Olfactory dysfunction, a common symptom among these patients, is an increasingly recognized condition that is associated with a reduced quality of life and major health outcomes. However, there are few studies on the association between olfactory function and asthma. We investigated the relationship between asthma and olfactory function. Patients and Methods: A total of 146 patients with asthma aged >18 years were retrospectively analyzed from August 2019 to February 2020. Olfactory function was assessed using the Sniffin' stick test or the YSK olfactory function test. We compared the clinical parameters of patients with olfactory dysfunction and patients with normosmia. Results: Of the total participants, 68 (46.6%) showed olfactory dysfunction (hyposmia, n=31; anosmia, n=37). The patients with olfactory dysfunction were older, had longer durations of asthma, and a higher proportion of those with poor general health, CRS, and nasal polyps compared to patients with normosmia. However, there were no significant differences in the socioeconomic status, lung function, asthma severity, and use of inhaled corticosteroids or intranasal steroids between the two groups. Age (odds ratio: 1.044, 95% confidence interval: 1.009-1.081, P=0.012), poor general health (3.304, P=0.018), CRS (2.589, P=0.021), and nasal polyps (3.306, 1.1-9.94, P=0.033) were significantly associated with olfactory dysfunction. Conclusion: Olfactory dysfunction was quite frequently observed in adults with asthma. Age, poor general health, CRS, and nasal polyps were significantly associated with olfactory dysfunction.

PM2.5 exposure and olfactory functions

“…Another possible explanation could be a self-selection away from areas with polluted areas among individuals with asthma. Since asthma has been shown to be associated with worse olfactory function (Rhyou et al 2021) this could potentially lead to bias towards the null in our study. A limitation in this study is that we do not have access to data regarding asthma for our participants; thus, we could not investigate the role of it in this study.…”

Brain response in asthma: the role of “lung-brain” axis mediated by neuroimmune crosstalk

“…Rhyou et al. conducted a clinical investigation on olfactory dysfunction in patients with asthma, which indicated that the incidence of olfactory disturbance in patients with CRS or AR associated with asthma was 56.5%, whereas the incidence of olfactory disturbance in patients with asthma alone was only 15.8% ( 10 ). Lacking direct research, the pathogenesis of asthma linked to olfactory dysfunction warrants further investigation.…”

“…Asthma is characterized by non-specific respiratory symptoms such as wheezing, shortness of breath, chest tightness, and episodic cough as the main clinical manifestations, which frequently occur at night and early in the morning, and its main pathogenesis is chronic immune-inflammatory response, airway hyperreactivity, reversible airflow limitation, and airway remodeling ( 6 , 7 ). Patients with asthma are often accompanied by neurological symptoms such as cognitive dysfunction, depression, anxiety, dysosmia, and sleep disorders, implying a brain response to asthma, which affects their quality of life, increases their economic burden, reduces the treatment sensitivity of asthma, increases the risk of asthma exacerbations, and forms a vicious cycle ( 8 – 10 ). Based on our previous summary of brain response in allergic rhinitis (AR) ( 11 ), a “lung–brain” crosstalk in asthma can be observed on the basis of neuro-immune mechanisms, that is, inflammatory factors generated during chronic inflammation in asthma can be transmitted upwards to the central nervous system, thereby stimulating associated brain regions to elicit one or more brain responses, transmitting response commands to peripheral nerves, activating such commands to release mediators such as neuropeptides and neurogenic trophic factors, worsening asthma symptoms through actions such as tracheal smooth muscle contraction, promoting the re-entry of immune inflammatory factors produced in the periphery to the brain, and exacerbating neurological symptoms caused by brain response ( 12 , 13 ).…”