Efficacy of olfactory-visual combined training on post-viral olfactory dysfunction: a randomized controlled trial.

objectiveOlfactory training (OT) involves repeated exposure to specific odors to stimulate the regeneration of olfactory pathways, improving the sense of smell. It is a widely used method for treating olfactory dysfunction. Post-viral olfactory dysfunction (PVOD) is a common cause of smell loss. In this study, we applied different OT methods to PVOD patients to identify the most effective training approach.

methodsA total of 120 PVOD patients (51 men, 69 women; mean age: 42.51 years; mean duration: 2.42 years) were included. They were randomly assigned to four groups: OT-4, OT-8, OT-4 + VS, and OT-0. OT was administered for six months. The OT-4 group sniffed four odors (rose, mint, coffee, and lemon) throughout the training.The OT-8 group sniffed rose, mint, coffee, and lemon for the first three months, then switched to orange, peach, jasmine, and strawberry for the remaining three months. The OT-4 + VS group followed the OT-4 training way but with added visual stimuli-patients were instructed to look at images corresponding to each odor while sniffing. The OT-0 group was assigned odorless paraffin oil throughout the study. Each 5-minute session, conducted twice daily, involved sniffing each odor for 10s followed by a 10-second interval. Olfactory assessments, including the Chinese Smell Identification Test (CSIT), olfactory Visual Analog Scale (VAS) scores, olfactory cleft endoscopy score (OCES), Questionnaire of Olfactory Disorders (QOD) scores, and Patient Health Questionnaire-9 (PHQ-9) scores, were conducted before training, at the mid-point, and at the end of training.

resultsAmong the 120 enrolled patients, 110 completed the study and 10 were lost to follow-up. Regardless of the number of scents used in the OT or whether visual stimulation was included, the three training groups showed significantly improved CSIT compared to the OT-0 group (p < 0.05). Among the three different OT methods, the OT-4 + VS group achieved the best olfactory results, and its olfactory improvement was the fastest among all four groups. There was no significant difference in CSIT between the OT-4 and OT-8 groups after training, but the OT-8 group showed a noticeable increase in olfactory function in the last three months. Regarding olfactory VAS scores, both OT-4 and OT-4 + VS showed significant improvement (p < 0.05 for all comparisons), while the OT-8 and OT-0 groups did not show improvement. There were no significant differences in OCES improvements between the groups. After six months of complete training, the QOD and PHQ-9 scores did not show any improvement in any of the four groups. CSIT and VAS scores for the OT-4, OT-8, and OT-4 + VS groups all showed a gradual improvement over time (p < 0.01 and p < 0.001), while the OCES, QOD, and PHQ-9 scores did not follow this trend. Higher education level was associated with a greater improvement in olfactory function (p < 0.01). Female patients exhibited better CSIT levels and subjective VAS scores than male patients (p < 0.01 and p < 0.001).

conclusionOlfactory-visual combined stimulation can rapidly and effectively improve the olfactory function in patients with post-viral olfactory disorders compared to traditional olfactory training. Education level and gender may influence the effectiveness of olfactory training.