Linked: People with loss of smell had behavioural, functional, and structural brain changes.
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A large body of studies has found how even mild COVID-19 impacts the brain of people. One the most common ailments seen among people who had COVID-19 was the loss of smell, otherwise called as anosmia. In most cases, people recover their sense of smell after a few weeks to months. Many studies have found that months after recovery from COVID-19, some people continued to experience neurological and cognitive effects. While persistent cognitive symptoms have been linked to brain alterations, patients recovering from mild COVID-19 without cognitive symptoms presented with cortical thickness alterations and changes in white matter integrity.

A small study from Chile recruited 73 adults with a mild to moderate COVID-19 without signs of respiratory failure and 27 people without any history of COVID-19. The 73 participants who had COVID-19 and recruited for the study had an average of nine months after diagnosis. Participants with COVID-19 and the control group were subjected to cognitive screening, a decision-making task, and MRI evaluations. The team used loss of smell and need for hospitalisation as proxies for potential markers of neurologic involvement and disease severity, respectively. The study, published in the journal Scientific Reports, has found that people who suffered from loss of smell had behavioural, functional, and structural brain changes.

 “Given the significant global incidence of COVID-19, identifying factors that can distinguish individuals at risk of developing brain alterations is crucial for prioritizing follow-up care,” the authors write. Since the anosmia “correlated with brain measures, including decreased functional activity during the decision-making task, thinning of cortical thickness in parietal regions, and loss of white matter integrity”, the authors say that anosmia could be used as a criterion when identifying at-risk populations for follow-up.

Of the 73 participants with COVID-19, 22 (30.1%) individuals reported experiencing varying degrees of attention and memory issues, which persisted at the time of the cognitive test administered as part of the study. Relatively minor indications were headache in seven participants, fatigue in six people, and four with persistently impaired sense of smell lasting, on average, 1.3 months. Of these patients, a complete loss of smell (anosmia) was experienced by 68% (29 participants), while 32% (14 participants) experienced differing degrees of changes in their sense of smell (hyposmia/microsmia). Both these categories were clubbed together as ‘patients with anosmia’.

While no significant differences in cognitive performance between groups based on COVID-19 diagnosis, anosmia, or hospitalisation requirements,  “intriguing patterns” emerged in behavioural task performance. Participants with a loss of smell displayed a distinct decision-making strategy characterised by more impulsive behaviour and were more likely to make a choice that is different when the earlier result was negative when performing a behavioural task. But the participants who were hospitalised displayed less strategic thinking and unlike those who were not hospitalised repeatedly made the same wrong choice.

Loss of smell was positively associated with decreased functional activity during the decision-making task, thinning of cortical thickness, and loss of white matter integrity. “Hence, anosmia could be a factor to be considered when identifying at-risk populations for follow-up,” the authors write.

“Only six patients present indicators of persistent olfactory deficit; thus, our results are not due to actual deficit. Hence, anosmia could serve as both a potential marker of virus-induced damage to neuronal tissues and a marker for individuals susceptible to brain damage,” the authors note.