Characteristics of subjective olfactory dysfunction and imaging features in patients with traumatic olfactory disorders: a retrospective case-control study.

BACKGROUND

Olfactory dysfunction caused by head trauma poses significant challenges in clinical diagnosis and treatment. The primary difficulty arises from direct injuries to olfactory-related brain tissues. Although imaging provides the most direct method to evaluate such injuries, there is no standardized international diagnostic criterion for olfactory dysfunction based on imaging. We designed this study to compare the subjective olfactory function differences and brain gray-matter (GM) and white-matter (WM) volume differences between patients with traumatic olfactory dysfunction and those with other types of olfactory dysfunction and to determine the characteristics of subjective olfactory dysfunction and imaging features in patients with traumatic olfactory disorders. The findings of this study can provide a theoretical basis for the diagnosis of traumatic olfactory disorders.

METHODS

This ethics committee-approved, retrospective case-control study included 56 patients with traumatic olfactory dysfunction (trauma group) and 45 patients with other types of olfactory dysfunction (e.g., postinfection, nasal inflammation, idiopathic disease). The "Sniffin' Sticks" olfactory function test was used to analyze the subjective olfactory function differences between the two groups, and voxel-based morphometry (VBM) was used to compare the GM volume (GMV) and WM volume (WMV) of brain regions between the two groups.

RESULTS

(I) There was no statistical difference in age distribution between the trauma group (41.55±11.77 years) and the control group (38.87±14.37 years; P>0.05). (II) The trauma group had significantly lower total scores and subtest scores on the Sniffin' Sticks olfactory test compared to the control group [odor threshold test (OT): 1.04±0.33 1.67±1.42; odor discrimination test (OD): 2.93±2.25 5.42±3.66; odor identification test (OI): 2.77±1.94 6.71±3.55; total scores: 6.74±3.91 13.81±7.63; all P values <0.05]. (III) Compared with the control group, the trauma group had significantly reduced GMV and WMV in the bilateral orbitofrontal cortex, bilateral anterior cingulate gyrus, bilateral cingulate gyrus, bilateral rectus gyrus, bilateral olfactory cortex, right superior frontal gyrus, bilateral insula, bilateral caudate nucleus, and bilateral thalamus [P<0.05]. (IV) There was a significant positive correlation between the odor identification function scores and GMV in certain brain regions (P<0.05), and the GMV in these regions was reduced in the trauma group compared to the control group.

CONCLUSIONS

Compared to patients with other types of olfactory dysfunction, patients with traumatic olfactory dysfunction have poorer subjective olfactory functions and more severe damage to olfactory-related brain regions, including the bilateral orbitofrontal cortex, anterior cingulate gyrus, cingulate gyrus, rectus gyrus, insula, and olfactory cortex. The olfactory nerve damage in these brain regions can be used as a basis for the diagnosis of traumatic olfactory disorders.