The condition affects the brain and spinal cord and can follow viral infections.
Infection with the coronavirus can cause delirium, stroke and nerve damage in 'a higher than expected number of patients', a study has found.
Experts from University College London have reported a 'concerning increase' amid the pandemic of a rare brain inflammation known to be triggered by viral infections.
Typically seen in children, acute disseminated encephalomyelitis — or 'ADEM', for short — affects the both the brain and spinal cord.
'We identified a higher than expected number of people with neurological conditions such as brain inflammation,' said paper author and consultant neurologist Michael Zandi of the University College London.
The appearance of these conditions, he added, '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.'
'Whether we will see an epidemic on a large scale of brain damage linked to the pandemic — perhaps similar to the encephalitis lethargica outbreak in the 1920s and 1930s after the 1918 influenza pandemic — remains to be seen.'
The researchers also found that other neurobiological complications — including delirium, stroke and nerve damage — appear to be associated with coronavirus.
In their study, Dr Zandi and colleagues studied 43 patients — aged from 16-85 — with both neurological symptoms and either confirmed or suspected COVID-19 that were treated at the National Hospital for Neurology and Neurosurgery in London.
According to the researchers, many of the patients did not experience any of the respiratory symptoms often associated with the coronavirus.
Among the cohort, the team identified 10 cases of temporary brain dysfunction with delirium, eight cases of strokes and eight cases with nerve damage.
There were also 12 cases of brain inflammation — with nine of such patients being diagnosed with ADEM.
Under normal circumstances, the London-based team said that they would only see around one adult patient with ADEM per month, on average — but that this figure has increased to at least one patient per week amid the pandemic.
SARS-CoV-2 — the virus which causes COVID-19 — was not detected in the brain or spinal fluid of any of the patients tested, however, the researchers said.
This, they explained, suggests that the virus did not directly cause the neurological symptoms and that some complications of COVID-19 'might come from [one's] immune response, rather than the virus itself.'
Further studies are needed to identify exactly why some COVID-19 patients are developing neurological complications, the researchers concluded.
'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,' said paper author and neurologist Ross Paterson, also of the University College London.
'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.'
'Our study advances understanding of the different ways in which COVID-19 can affect the brain,' added paper author and neurologist Rachel Brown, also of the University College London.
Such knowledge, she added, 'will be paramount in the collective effort to support and manage patients in their treatment and recovery.'
'This paper adds to the emerging evidence for a wide range of potentially severe neurological complications of COVID-19 beyond its effects on the respiratory system,' said neuroscientist Timothy Nicholson, who was not involved in the study.
The work, the King’s College London researcher added, highlights the importance of future research to assess how common these neurological and psychiatric complications are [and] what mechanisms are causing them.'
This, he explained, could lead to methods to 'treat them better and improve longer term outcomes.'
The full findings of the study were published in the journal Brain.