Abstract

Relevance: During the period of studying the impact of the SARS-CoV-2 virus – both during the pandemic and after its decline – a wide range of manifestations affecting various organs and systems has been investigated. The virus has undergone mutations, and the clinical presentation of the disease has changed; however, its impact has remained diverse and sufficiently pronounced. However, some of the main manifestations, expressed to varying degrees, have remained unchanged – namely, disorders of the cardiovascular and nervous systems. Sensory disorders in COVID-19 have also become more widespread, including impairments of hearing, smell, and taste, as well as disturbances of balance function.

The purpose of this study was to investigate indicators of brain bioelectrical activity according to EEG data in individuals who have recovered from COVID-19 and have sensory disorders of varying severity.

Materials and methods: An analysis of questionnaire data, medical history, and complaints was conducted in 120 patients who had recovered from COVID-19 and exhibited sensory disorders. The patients were divided into two groups. Group 1 included 74 patients with moderate or less pronounced hearing impairments after COVID-19. Group 2 consisted of 46 patients who predominantly experienced a more severe course of the infection and developed persistent, progressive hearing disorders accompanied by changes in the nervous system. The control group comprised 15 apparently healthy individuals who had not had COVID-19 and reported no complaints related to sensory system dysfunction.

   Electroencephalography (EEG) was performed using a computer-based electroencephalograph manufactured by DX-Systems (Ukraine). Baseline EEG recordings were obtained, followed by functional tests, including eye opening-closing, rhythmic photic stimulation, and three-minute hyperventilation.

Results and discussion: A qualitative and quantitative analysis (determination of the percentage of the main EEG rhythms) of EEG data was performed in individuals from the study groups who had recovered from COVID-19 and presented with sensory disorders of varying severity.

   In the examined individuals with a history of COVID-19, deviations from normal EEG patterns were identified both in baseline recordings and during functional tests, including photic stimulation and hyperventilation. Qualitative analysis of EEG results in these patients revealed alterations in the brain’s bioelectrical activity manifested as desynchronization and disorganization of the main rhythms, along with an increase in slow-wave activity. These signs of EEG rhythm disorganization became more pronounced during functional tests, particularly in the frontal regions, which indicates functional disturbances of the central nervous system involving cortical as well as deeper diencephalic and diencephalic-brainstem structures in this category of patients. Moreover, such changes were more prominent in patients of Group 2, who demonstrated persistent and more severe sensory disorders after COVID-19.

In individuals of Group 2, quantitative indicators of the percentage content of the main EEG rhythms were more pronounced in the frontal and occipital leads, and the percentage values of several rhythms differed significantly (p<0,05) not only from those of the control group but also from Group 1. In the frontal and temporal leads, the differences between study groups were not statistically significant; however, in both cases, there was a significant increase in rhythm content compared with control values.

The greatest increase in delta activity was observed in both study groups of post-COVID-19 patients with sensory disorders in the frontal leads, both in baseline recordings and during functional tests.

A significant increase in beta activity and a decrease in alpha-wave representation were also detected. These changes were particularly pronounced in the occipital leads, both in baseline conditions and during hyperventilation.

Thus, individuals who recovered from COVID-19 and have sensory disorders demonstrate a redistribution of the main EEG rhythms, characterized by increased slow-wave activity and reduced alpha-rhythm representation. This tendency was more pronounced in Group 2 patients with persistent and severe sensory impairments.

Conclusions:

Central nervous system alterations in patients with sensory system disorders after COVID-19 frequently manifest as a significant (P < 0,05) increase in delta and beta activity, indicating cortical rhythm desynchronization and involvement of diencephalic–brainstem structures. These changes are more pronounced in patients with persistent and marked sensory impairments.

Signs of dysfunction within the diencephalic-brainstem structures of the brain, combined with increased slow-wave activity, represent unfavorable prognostic factors for the development of more severe sensory disorders resulting from COVID-19.

Keywords: bioelectric activity of the brain, electroencephalography, hearing, auditory system, COVID-19.