COVID-related loss of smell tied to changes in the brain, finds study

Cognitive function and the health of the brain may be impaired due to COVID-19, even after mild or moderate infection. Given its global prevalence, affecting tens of millions, understanding which patients are at the greatest risk for cognitive and neurological complications is paramount. While cognitive impairments and brain abnormalities have been described, mechanisms and risk factors are poorly understood. Anosmia has been suggested as a marker of these complications. Here, the study assessed the cognitive and neurological sequelae in relation to anosmia and the requirement for hospitalization in 73 adults with mild-to-moderate COVID-19 in comparison with 27 controls.

In the present study, 100 individuals were assessed: 73 recovered adults from mild-to-moderate COVID-19 and 27 infected with other agents, with no history of COVID-19. Patients did not present respiratory failure. Cognitive screening was performed, a decision-making task was evaluated, and structural MRI was performed in all participants. The occurrence of anosmia and the need for hospitalization for the study were evaluated as possible risk factors related to cognitive and brain changes.

There were no significant differences in cognitive performance and age across groups. The study was designed to relate anosmia, impulsive decision-making, and brain structural changes.

Key Findings

• Anosmic patients presented even a greater number of impulsive decision-making behaviors, especially to changes in probability while performing decision-making tasks.

• The correlation between anosmia and impulsive shifts was significant:(r = -0.26, p = 0.001). Those having anosmia were more likely to make impulsive decisions when the scenarios changed.

• A higher prevalence of perseverative choices was found in hospitalized patients.

• A statistically significant correlation was identified regarding hospitalizations and the patients' perseverative behavior (r = 0.25, p = 0.003).

• MRI and anosmia were correlated with abnormal reduction in functional activity during the choice phase of decision-making, reduced thinning of cortical thickness in parietal regions, and reduced loss of white matter integrity.

• Such results indicate that olfactory function has to be considered not as a narrow sensory function but possibly in the context of wide-ranging brain changes likely to affect cognitive function.

• This study, therefore, highlights the importance of anosmia being included in any workup approach directed toward identification of patients who are likely to experience late sequelae in cognitive and brain health after COVID-19. Such information might help practicing clinicians guide relevant rehabilitation for these patients.

These findings further underscore the role of anosmia as a harbinger of potential cognitive and neurological sequelae in COVID-19 recovery. The interaction between anosmia, impulsivity, and brain changes explains the overall impact of COVID-19 on brain function. This finding can suggest that anosmia could be of greater usefulness as a marker in the selection of subjects who should be offered further controls or very early interventions to prevent complications of long-term cognitive decline.

Anosmia, one of the common symptoms of COVID-19, is related to cognitive and brain changes, thereby making it a major risk factor for follow-up care. Notably, these findings of this study have shown that patients with anosmia link impulsive decision-making behavior to brain changes featured by reduced functional activity together with structural integrity. Identification of anosmia in post-COVID patients may help in prioritizing those needing closer follow-ups in cognitive and neurological terms, finally aiding better long-term outcomes.

Reference:

Kausel, L., Figueroa-Vargas, A., Zamorano, F., Stecher, X., Aspé-Sánchez, M., Carvajal-Paredes, P., Márquez-Rodríguez, V., Martínez-Molina, M. P., Román, C., Soto-Fernández, P., Valdebenito-Oyarzo, G., Manterola, C., Uribe-San-Martín, R., Silva, C., Henríquez-Ch, R., Aboitiz, F., Polania, R., Guevara, P., Muñoz-Venturelli, P., … Billeke, P. (2024). Patients recovering from COVID-19 who presented with anosmia during their acute episode have behavioral, functional, and structural brain alterations. Scientific Reports, 14(1), 1–14. https://doi.org/10.1038/s41598-024-69772-y