The effect of olfactory training on odor identification in patients with traumatic anosmia

Background This study investigates the effect of olfactory training on odor identification in patients with traumatic anosmia. Methods Patients with a clear history of loss of smell after head injury, and whose phenyl ethyl alcohol (PEA) odor detection thresholds remained at -1 after steroid and zinc treatment, were included in this study between July 2016 and July 2018. They were randomly divided into 2 groups, with patients in the 4-odorant group given 4 bottles of PEA, lemon, eucalyptus, and clove oils and those in the PEA group given a bottle of PEA for 6-month olfactory training. After 3-month and 6-month training, the olfactory function was evaluated by both the PEA threshold test and the traditional Chinese version of the University of Pennsylvania Smell Identification Test (UPSIT-TC). Magnetic resonance imaging was performed to measure the volume of olfactory bulbs after training. Results There were 45 patients completing 4-odorant training and another 45 completing PEA training. The birhinal PEA threshold decreased significantly in both groups after 6-month training, but the decrease was not significantly different between the 2 groups. The UPSIT-TC score increased significantly in the PEA group but not in the 4-odorant group. The volume of olfactory bulbs was not significantly different between these 2 groups. Conclusion Our results show that olfactory training can slightly improve odor threshold levels in patients with traumatic anosmia, but did not improve the odor identification ability. Nevertheless, clinical improvement or benefit in quality of life from olfactory training needs further investigation.