Scientists have raised the prospect of a brain damage "epidemic" after detecting an increase in life-threatening inflammation linked to coronavirus.
Experts have described a fourfold increase since the start of the crisis in acute disseminated encephalomyelitis (ADEM) - a rare and sometimes fatal complication normally found in children.
Some of the patients, all of whom had confirmed or suspected Covid-19, were not otherwise suffering serious respiratory symptoms.
Writing in the journal 'Brain', the scientists at University College London's Institute of Neurology called for systematic surveillance of complications as a result of the virus.
They highlighted the outbreak of encephalitis lethargica in the years after the 1918 Spanish Influenza pandemic. The so-called "sleepy sickness", which left some victims in a statue-like condition, motionless and speechless, was thought to affect several million.
The new study identified 43 suspected or confirmed coronavirus sufferers aged between 16 and 85 who were treated at the specialist unit in University College Hospital in London. Researchers identified 10 cases of transient encephalopathies - a temporary brain dysfunction - with delirium, which corresponds with other studies finding evidence of delirium with agitation.
There were also 12 cases of brain-inflammation, eight cases of strokes, and eight others with nerve damage, mainly Guillain-Barre syndrome.
Nine of the 12 cases of those with brain inflammation conditions were diagnosed with ADEM, which is known to be triggered by viral infections.
The team in London normally sees about one adult patient with ADEM per month, but that increased to at least one per week.
Dr Ross Paterson, joint first author of the paper, said: "Given that the disease has only been around for a matter of months, we might not yet know what long-term damage Covid-19 can cause.
"Doctors need to be aware of possible neurological effects, as early diagnosis can improve patient outcomes. People recovering from the virus should seek professional health advice if they experience neurological symptoms," he added.
The virus causing Covid-19, SARS-CoV-2, was not detected in the cerebrospinal brain fluid of any of the patients tested, suggesting the virus did not directly attack the brain to cause the neurological illness.
In some patients, the researchers found evidence the brain inflammation was likely caused by an immune response to the disease.
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