Heterogeneous Damage to the Olfactory Epithelium in Patients with Post-Viral Olfactory Dysfunction

Objectives: Post-viral olfactory dysfunction (PVOD) is a neurogenic disorder caused by a common cold virus. Based on the homology of deduced amino acid sequences, olfactory sensory neurons (OSNs) in both mice and humans express either class I or class II odorant receptor genes encoding class I and class II OSNs. The purpose of this study was to determine whether OSN damage in PVOD occurs uniformly in both neuron types. Materials and methods: The characteristics of PVOD patients were compared with those of patients with chronic rhinosinusitis (CRS) or post-traumatic olfactory dysfunction (PTOD). Briefly, subjects underwent orthonasal olfaction tests using five different odors (T & T odors) and a retronasal olfaction test using a single odor (IVO odor). The regions in the mouse olfactory bulb (OB) activated by the T & T and the IVO odors were also examined. Results: Multivariate analysis of 307 cases of olfactory dysfunction (PVOD, 118 cases; CRS, 161 cases; and PTOD, 28 cases) revealed that a combination of responses to the IVO odor, but not to the T & T odors, is characteristic of PVOD, with high specificity (p < 0.001). Imaging analysis of GCaMP3 mice showed that the IVO odor selectively activated the OB region in which the axons of class I OSNs converged, whereas the T & T odors broadly activated the OB region in which axons of class I and class II OSNs converged. Conclusions: A response to T & T odors, but not IVO odor, in PVOD suggests that class I OSNs are injured preferentially, and that OSN damage in PVOD may occur heterogeneously in a neuron-type-dependent manner.

Automated summary

The objective of this study was to determine if olfactory sensory neurons are uniformly damaged in PVOD. Comparing PVOD patients with CRS and PTOD patients, it was found that a response to a single odor is characteristic of PVOD, while there were no significant abnormalities in the response to five different odors. In mouse experiments, it was found that a single odor selectively activated one type of sensory neurons, while five different odors activated both types of sensory neurons simultaneously.