Clinical characteristics and associated factors of qualitative olfactory dysfunction

Background: Although interest in qualitative olfactory dysfunction (OD), including parosmia and phantosmia, has been increasing since the COVID-19 pandemic, little is known about the clinical characteristics and associated factors of qualitative OD. Methods: Adult patients with subjective smell disturbance who underwent both the olfactory questionnaire and psychophysical olfactory function test were retrospectively enrolled. Demographic and clinical characteristics were analysed according to the presence or absence of parosmia or phantosmia. Results: Among a total of 753 patients with self-reported OD, 60 (8%) and 167 (22.2%) patients reported parosmia and phantosmia, respectively. Younger age and female sex were related to both parosmia and phantosmia. The frequency of parosmia was significantly higher in patients with post-viral OD (17.9%) than in patients with the sinonasal disease (5.5%), whereas that of phantosmia was not different according to aetiologies of OD. Patients with COVID-19 had significantly younger ages and higher TDI scores than those with other viral infections. Remarkably, patients with parosmia or phantosmia had significantly higher TDI scores than those without but experienced more disruption in daily life. In the multivariate analysis, younger age and higher TDI score were identified as independent factors associated with both parosmia and phantosmia, while the viral infection was associated with parosmia but not with phantosmia. Conclusions: Patients with OD who have parosmia or phantosmia have higher odour sensitivity than those who do not, but experience more deterioration in the quality of life. Viral infection is a risk factor for parosmia but not for phantosmia.