The patient’s chart appeared unremarkable at first glance. He took no medications and had no history of chronic conditions. He had been feeling fine, hanging out at home during the lockdown like the rest of the country, when suddenly, he had trouble talking and moving the right side of his body. Imaging showed a large blockage on the left side of his head.

Oxley gasped when he got to the patient’s age and covid-19 status: 44, positive.

The man was among several recent stroke patients in their 30s to 40s who were all infected with the coronavirus. The median age for that type of severe stroke is 74.

As Oxley, an interventional neurologist, began the procedure to remove the clot, he observed something he had never seen before. On the monitors, the brain typically shows up as a tangle of black squiggles — “like a can of spaghetti,” he said — that provide a map of blood vessels. A clot shows up as a blank spot. As he used a needlelike device to pull out the clot, he saw new clots forming in real-time around it.