Anosmia in COVID-19: A Marker for Brain Alterations in Recovered Patients

Key Takeaways

• New research highlights anosmia (loss of smell) as a potential marker for brain alterations in post-COVID patients.
• The study found significant changes in brain structure and function in patients who experienced anosmia during COVID-19.
• Patients with anosmia exhibited more impulsive decision-making behaviors and structural brain changes, including reduced white matter integrity.
• These findings underscore the importance of neurological follow-ups for patients who experienced anosmia during their COVID-19 infection.

Introduction

The COVID-19 pandemic has brought significant attention to the long-term effects of the virus, commonly referred to as “long COVID.” While much focus has been placed on respiratory and cardiovascular issues, emerging evidence suggests that COVID-19 can also cause lasting brain alterations. A new study, published in Nature Scientific Reports, explores the neurological impacts of COVID-19, particularly in patients who experienced anosmia—complete or partial loss of smell—during their infection.

Given that anosmia is a widely reported symptom in COVID-19 patients, understanding its potential as a marker for long-term neurological impacts could have significant implications for public health follow-up care. This article delves into the study’s findings, which suggest that patients with anosmia may be at higher risk for brain alterations, even if their overall infection was classified as mild or moderate.

The Study: A Focus on Anosmia and Brain Alterations

Researchers conducted a comprehensive study involving 73 adults who had mild to moderate COVID-19 without respiratory failure, compared to 27 participants with other respiratory infections. Cognitive screening, decision-making tasks, and MRI evaluations were employed to assess brain function and structure in these patients.

The study’s results revealed that patients who experienced anosmia during their acute COVID-19 episode showed notable differences in brain activity and decision-making behaviors. These patients were more likely to make impulsive decisions after negative outcomes in tasks requiring cognitive flexibility. This impulsivity was linked to brain alterations such as reduced functional activity in decision-making areas, cortical thinning in the parietal region, and decreased white matter integrity.

Anosmia as a Neurological Marker

Anosmia is not just a symptom of COVID-19; it is also seen in neurological diseases like Alzheimer’s, Parkinson’s, and Huntington’s disease. The researchers found that anosmia in COVID-19 patients could serve as a preclinical indicator of brain alterations. The brain scans revealed that patients with anosmia exhibited a thinning of the cortex in parietal areas and showed disruptions in white matter integrity, particularly in tracts like the corticospinal tract and the arcuate fasciculus. For reference, the corticospinal tract contributes to the control of voluntary movement from the neck to the feet, while the arcuate fasciculus is critical for understanding and forming speech, word retrieval and forming appropriate responses.

The presence of these brain changes raises concerns that anosmia during COVID-19 may reflect a broader vulnerability to brain damage, possibly through the virus’s interaction with the olfactory system. While the study could not definitively prove that COVID-19 directly infects brain tissue, it supports the theory that anosmia might signal a patient’s susceptibility to long-term neurological effects.

Behavioral and Cognitive Effects

In addition to structural brain changes, the study found behavioral differences among patients with anosmia. These individuals tended to exhibit more impulsive decision-making strategies, especially when adapting to changing environments or new information. This impulsivity, while advantageous in the short term, may indicate a deeper underlying issue with cognitive flexibility—a crucial function for daily decision-making and adapting to unexpected situations.

Interestingly, while the anosmia group showed impulsive shifts in decision-making, patients who required hospitalization for COVID-19 were more likely to demonstrate perseverative behaviors. This means they were slower to adapt to new information, indicating that hospitalization might be linked to different forms of cognitive impairment.

Implications for Public Health and Follow-Up Care

The findings from this study suggest that anosmia should not be overlooked as a mere symptom of COVID-19 but should instead be considered a possible indicator of more serious neurological alterations. For public health professionals and clinicians, this means that patients who experienced anosmia during COVID-19 may require neurological follow-ups to monitor for potential long-term effects on brain function.

With millions of COVID-19 survivors worldwide, identifying patients at higher risk for brain alterations is crucial. Prioritizing those who experienced anosmia for cognitive and neurological screening could help detect early signs of long COVID-related brain damage, allowing for timely interventions that may mitigate long-term cognitive decline.

Long-Term Cognitive and Structural Changes

Even in those without severe respiratory symptoms, long term, yet subtle changes in brain structure and function were detected months after recovery. This includes thinning in areas of the brain associated with memory, decision-making, and sensory processing.

Other studies have supported these findings, showing that patients recovering from even mild COVID-19 infections can experience long-term neurological symptoms, including memory problems, brain fog, and mood disturbances. These changes have been linked to alterations in white matter integrity and cortical thickness, further underscoring the need for comprehensive neurological evaluations in post-COVID care.

Future Research Directions

The study authors recommend further research to clarify the exact mechanisms behind the brain alterations observed in patients with anosmia. One potential avenue for exploration is the role of inflammation in these changes, as neuroinflammation has been linked to both anosmia and cognitive decline in long COVID patients. Additionally, researchers are exploring whether certain genetic factors, such as variations in the UGT2A1/UGT2A2 gene, could predispose individuals to anosmia and subsequent brain alterations.

Future studies may also investigate how different COVID-19 variants impact neurological health, as early evidence suggests that some variants may be more likely to cause anosmia and other neurological symptoms.

Conclusion

As the global community continues to recover from the acute phases of the COVID-19 pandemic, attention is shifting towards understanding the long-term effects of the virus on various aspects of health. This new study provides critical insight into how  a common symptom of COVID-19 may be an indicator of brain alterations, even in patients who experienced mild to moderate infections.

The findings underscore the importance of recognizing anosmia as more than a temporary sensory loss. For healthcare providers and public health professionals, these insights highlight the need for continued monitoring and follow-up care for patients with a history of anosmia during their COVID-19 infection, as well as underscore the importance of COVID-19 prevention efforts even long after the pandemic has been declared “over”.

The featured image for this article is by Jose Luis Navarro, and gathered from kumn.org