Exploring the Neurological manifestations of COVID-19
Coronavirus disease 2019, popularly abbreviated as COVID-19 is a highly contagious infection caused by the novel coronavirus called Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). COVID-19 is primarily characterised by severe respiratory pathology. Current research has discovered a number of extrapulmonary manifestations of COVID-19, neuro-psychiatric illness being one of them.
COVID-19 can have multisystemic effects, including a wide spectrum of psychiatric and neurological disorders. A considerable number of patients have reported persistent neurological manifestations, from milder symptoms such as headaches, hyposmia (decreased sense of smell), hypogeusia (loss of taste), and fatigue to more severe conditions including sleep disorders, pain, cognitive impairment, and in extremely rare cases, Guillain-Barré syndrome (a condition in which body's immune system attacks your nerves). This phenomenon is popularly known as “long covid”. Delirium (mental confusion and emotional disruption) is the most common symptom. In some people, response to the novel coronavirus has been shown to increase the risk of stroke, dementia, muscle and nerve damage, encephalitis, and vascular disorders.
How does an infection that primarily affects the respiratory tract affect the nervous system? To understand that, let’s venture into the pathophysiology of COVID-19.
How does SARS-CoV-2 access the Central Nervous System?
Angiotensin Convertase Enzyme-2 has been identified as a functional receptor for SARS-CoV-2. The S protein of coronavirus binds to these receptors to initiate the host cell invasion. The thin tissue forming the outer layer of the nasal cavity, called the pulmonary epithelium has the highest concentration of ACE-2 receptors. Hence, researchers have hypothesised that SARS-CoV-2 may access the central nervous system through the nasal mucosa or olfactory bulb via retrograde axonal transport (the system that conveys materials from the axon terminal to the cell body).
The innate and adaptive immune responses activated by SARS- CoV-2 infection lead to uncontrolled inflammatory responses and ultimately cause the cytokine storm (excessive release of pro-inflammatory signalling molecules: cytokines). This cytokine storm might potentially damage the brain vasculature and the blood–brain barrier, especially in case of multi-organ dysfunction seen in critical cases.
Neurological Manifestations of COVID-19:
About 30% of COVID-19 patients show neuropsychiatric symptoms. Commonly observed long-term psychological effects include anxiety, post-traumatic stress disorder and depression.
Dr. Fernanda Crunfli et.al. recruited patients to undergo MRI scans and neuropsychiatric interviews to analyze their memory and cognitive functions. About 28% of patients showed signs of anxiety; 20% showed signs of depression; 28% showed abnormal logical memory performance. Upon correlating cortical thickness changes to neuropsychological evaluation, the team found that thinner cortex affected verbal memory, suggesting COVID-19 can affect brain structure and alter brain functions.
According to researchers at Columbia University, the interaction between blood clots and inflammation caused by COVID-19 resembles the kind of traumatic brain injury seen in footballers. People with traumatic brain injury may suddenly experience personality changes, sometimes becoming aggressive or suicidal. Dr Boldrini is currently measuring the amount of microglia, neuronal damage, and inflammatory markers (set of biomarkers that are used clinically to assess for the presence of active inflammation) that are present in the brains of patients. If it is found that inflammation is causing psychiatric symptoms, they would modulate inflammatory markers to slow down the persistent inflammatory response. The approach is similar to how drugs dampen the immune response in autoimmune disorders.
Do Neurological manifestations indicate that SARS-CoV-2 is neurovirulent in nature? It is too soon to conclude that. But it is safe to assume that the pandemic has had adverse physiological and psychological effects on those affected. It is important to acknowledge this anomaly and seek requisite help from doctors and mental health professionals.
You can read more about the latest weekly updated literature on the neurological and neuropsychiatric manifestations of COVID-19, here - https://blogs.bmj.com/jnnp/2020/05/01/the-neurology-and-neuropsychiatry-of-covid-19/