Exploratory Study on Chemosensory Event-Related Potentials in Long COVID-19 and Mild Cognitive Impairment: A Common Pathway?

Olfactory event-related potentials (OERPs) and trigeminal event-related potentials (TERPs) in subjects after Covid-19 infection: single-center prospective study

OBJECTIVES

Olfactory dysfunction (OD) is a common symptom associated with Covid-19. During the Covid-19 pandemic, the importance of psychophysical olfactory tests and electrophysiological olfactory assessment increased. The purpose of the study was to analyze the psychophysical olfactory tests and the post-covid curves of olfactory event-related potentials (OERPs) and trigeminal event-related potentials (TERPs).

METHODS

The prospective study included 98 subjects (62 females / 36 males). The average age was 42 years (range 21-84 years). Group I (n = 77) contained participants who had been infected with Covid-19. They were enrolled in the study at least 1 year after Covid-19. Group II (n = 21) was the healthy normosmic control group.

RESULTS

In Group I, the OERPs of 18% participants were absent. Patients in Group I were statistically more likely to have an absence of OERPs (p = 0.036) than subjects in Group II. We did not detect a statistical difference in amplitudes and latencies of the OERPs between Group I and Group II. In Group I, N1 latency of the TERPs was significantly longer (p = 0.002) than in Group II. The amplitude of the N1-P2 interval of the TERPs was significantly lower (p = 0.025) in Group I than in Group II. According to the psychophysical Sniffin stick identification test, hyposmia was detected in 39% in Group I versus 0% in the control Group II.

CONCLUSION

OD is a common post-covid symptom. The presence of OERPs is a significant prognostic factor for olfactory function after Covid 19. We detected a lower percentage of absence of OERPs after Covid-19 compared to the previously published studies of post-viral OD and post-infectious OD. For TERPs, we detected a longer N1 latency and a lower amplitude for the N1-P2 interval after Covid-19. OERPs and TERPs can be considered valid biomarkers to evaluate the progress of post-covid OD.

Evaluation of Mild Cognitive Impairment through Perientorhinal/Hippocampal Imaging and Comprehensive Neuropsychological and Psychophysical Assessment

Mild cognitive impairment (MCI) is a significant concern as it is a risk factor for AD progression, and early detection is vital in order to delay dementia onset and enable potential therapeutic interventions. Olfactory impairment is recognized as a predictive biomarker in neurodegenerative processes. The aims of this study were to explore the degree of entorhinal cortical atrophy (ERICA) and the severity of MCI symptoms; to analyze magnetic resonance imaging (MRI) results for the entorhinal cortex, parahippocampal gyrus, peri entorhinal cortex, and the cerebellar tentorium; and to perform a comprehensive neuropsychological and psychophysical assessment. The main results highlighted that in our sample-multidomain amnesic MCI patients with hyposmic symptomatology-we found that ERICA scores were associated with the severity of anxiety symptomatology. One possible hypothesis to explain this observation is that anxiety may contribute to neurodegenerative processes by inducing chronic stress and inflammation. Future research should consider the longitudinal development of neuropsychological scores, anxiety disorders, and brain atrophy to determine their potential predictive value for MCI progression. These findings suggest the importance of psychological factors in MCI progression and the utility of neuropsychological assessment alongside neuroimaging techniques for early detection and follow-up in MCI patients.

Trigeminal function in patients with COVID-associated olfactory loss

PURPOSE

Olfactory dysfunction (OD) can be a long-term consequence of various viral infections, including COVID-19. Dysfunction includes hyposmia/anosmia and parosmia (odor distortions). Interactions of the virus with the olfactory nerve have been extensively researched, but little is known about the interactions of the intranasal trigeminal nerve system in modulating this sensory loss.

METHODS

We investigated intranasal trigeminal function across COVID-19 OD patients with and without parosmia compared to normosmic controls, to determine whether (1) post-viral hyposmia and/or (2) post-viral hyposmia with parosmia is associated with altered trigeminal function. OD patients (n = 27) were tested for olfactory function using the extended Sniffin' Sticks olfactory test and for trigeminal function through three methods-odor lateralization, subjective ratings of nasal patency, and ammonium vapor pain intensity ratings. This group was subsequently compared to controls, normosmic subjects (n = 15).

RESULTS

Our findings revealed that post-COVID OD patients without parosmia experienced decreased sensitivity in ammonium vapor pain intensity ratings and odor lateralization scores-but similar nasal patency ratings-compared to normosmic controls. There were no significant differences in trigeminal function between OD patients with and without parosmia.

CONCLUSIONS

Based on our results, we conclude that the trigeminal nerve dysfunction may partially explain post-viral OD, but does not seem to be a major factor in the generation of parosmia pathophysiology.