Age and pre-existing conditions increase risk of stroke amon
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Fourteen out of every 1,000 COVID-19 patients admitted to hospital experience a stroke, a rate that is even higher in older patients and those with severe infection and pre-existing vascular conditions, according to a report published this week.

A team of researchers at the Stroke Research Group, University of Cambridge, carried out a systematic review and meta-analysis of published research into the link between COVID-19 and stroke.

In total, the researchers analysed 61 studies, covering more than 100,000 patients admitted to hospital with COVID-19. The results of their study are published in the International Journal of Stroke.

The researchers found that stroke occurred in 14 out of every 1,000 cases. The most common manifestation was acute ischemic stroke, which occurred in just over 12 out of every 1,000 cases. Brain haemorrhage was less common, occurring in 1.6 out of every 1,000 cases. Most patients had been admitted with COVID-19 symptoms, with stroke occurring a few days later.

Age was a risk factor, with COVID-19 patients who developed stroke being on average (median) 4.8 years older than those who did not. COVID-19 patients who experienced a stroke were on average (median) six years younger than non-COVID-19 stroke patients. There was no sex difference and no significant difference in rates of smokers versus non-smokers.

Pre-existing conditions also increased the risk of stroke. Patients with high blood pressure were more likely to experience stroke than patients with normal blood pressure, while both diabetes and coronary artery disease also increased risk. Patients who had a more severe infection with SARS­CoV­2—the coronavirus that causes COVID-19—were also more likely to have a stroke.

The researchers found that COVID-19-associated strokes often followed a characteristic pattern, with stroke caused by blockage of a large cerebral artery, and brain imaging showing strokes in more than one cerebral arterial territory. They argue that this pattern suggests cerebral thrombosis and/or thromboembolism are important factors in causing stroke in COVID-19. COVID-19-associated strokes were also more severe and had a high mortality.

The researchers say there may be several possible mechanisms behind the link between COVID-19 and stroke. One mechanism might be that the virus triggers an inflammatory response that causes thickening of the blood, increasing the risk of thrombosis and stroke. Another relates to ACE2—a protein 'receptor' on the surface of cells that SARS-CoV-2 uses to break into the cell. This receptor is commonly found on cells in the lungs, heart, kidneys, and in the lining of blood vessels—if the virus invades the lining of blood vessels, it could cause inflammation, constricting the blood vessels and restricting blood flow.

A third possible mechanism is the immune system over-reacting to infection, with subsequent excessive release of proteins known as cytokine. This so-called 'cytokine storm' could then cause brain damage.