Trends in Olfactory Threshold Test Results and Limits of Olfactory Testing in Patients with Parosmia

Parosmia poses a clinical challenge due to a lack of established testing methods, leading to underestimated self-reported symptoms. This study investigated olfactory threshold trends, aiming to highlight parosmia prevalence, analyze threshold patterns, and assess diagnostic potential in current olfactory testing.

A total of 407 patients who visited our olfactory clinic from April 2009 to September 2015 were categorized into parosmia and non-parosmia groups based on initial visit questionnaires. The Jet Stream T&T Olfactometer measured olfactory thresholds, including mean detection and recognition thresholds, and the left-right detection threshold difference. Patient characteristics such as gender, age, time from symptom onset to hospital visit, and smoking status were compared. The study also aimed to diagnose parosmia with olfactory identification ability tests such as Open Essence and the gap between T&T detection and recognition thresholds.

Parosmia prevalence was 18%, with a significant gender difference and a shorter onset-to-visit duration in the parosmia group. Post-traumatic and post-infectious olfactory dysfunctions exhibited higher parosmia prevalence. Olfactory threshold testing revealed significantly lower average detection (p = 0.014) and recognition (p = 0.005) thresholds in the parosmia group, with a left-right difference in detection thresholds (p = 0.012). No significant differences were found in identification ability tests. Results suggest that preserved sense of smell is crucial for perceiving parosmia symptoms.

Parosmia was observed in 18% of patients, more commonly among females and often following trauma or infection. It presents diagnostic challenges as patients tend to maintain olfactory thresholds, making subjective assessments essential for diagnosis. The significant left-right differences in detection thresholds suggest that olfactory lateralization may play a role in the manifestation of parosmia symptoms. Our findings suggest that a unilateral occlusion test, which identifies which nostril is more likely to cause parosmia, could allow for more targeted treatment.