Acute disseminated encephalomyelitis (ADEM) affects the brain and spinal cord and is typically seen in children.
It often follows on from a minor infection such as a cold – activating immune cells to attack the fatty protective coating covering the nerves.
But researchers from University College London said there has been a “concerning increase” in ADEM among adults during the pandemic.
Based on their findings, published in the journal Brain, the researchers say clinicians need to be aware of possible neurological effects in order to make an early diagnosis and improve patient outcomes.
Dr Michael Zandi, of UCL Queen Square Institute of Neurology and University College London Hospitals NHS Foundation Trust, who was a senior author on the study, said: “We identified a higher than expected number of people with neurological conditions such as brain inflammation, which did not always correlate with the severity of respiratory symptoms.
“We should be vigilant and look out for these complications in people who have had Covid-19.”
He said it remains to be seen “whether we will see an epidemic on a large scale of brain damage linked to the pandemic”.
The researchers also found other neurobiological complications, such as delirium, stroke and nerve damage, to be associated with the disease.
According to the team, some of the 43 patients studied did not experience respiratory symptoms.
These patients, who had either confirmed or suspected Covid-19, were aged between 16 and 85 and were treated at the National Hospital for Neurology and Neurosurgery, UCLH.
The researchers identified ten cases of temporary brain dysfunction with delirium, eight cases of strokes, and eight others with nerve damage.
There were also 12 cases of brain inflammation, nine of which were diagnosed with ADEM.
Sars-CoV-2, the virus whichcauses Covid-19 disease, was not detected in the brain and spinal fluid of any of the patients tested, the researchers said.
They added that the team also found evidence of brain inflammation being caused by an immune response to the disease, “suggesting that some neurological complications of Covid-19 might come from the immune response rather than the virus itself”.
The researchers said further studies are needed to identify why some Covid-19 patients are developing neurological complications.
Dr Ross Paterson, of UCL Queen Square Institute of Neurology, and joint first author on the study, 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 needs 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.”
ADEM’s symptoms resemble the symptoms of multiple sclerosis.
It affects about eight per 1,000,000 people per year and is most reported in children and adolescents, with the average age around five to eight years old.
The disease affects males and females almost equally and shows seasonal variation, with higher incidence in winter and spring months which may coincide with higher viral infections.
The mortality rate may be as high as 5 per cent but full recovery is seen in 50 to 75 per cent of cases. The average time to recover from ADEM flare-ups is one to six months.