The somewhat mysterious inflammatory syndrome that affects certain children with the coronavirus often causes neurological symptoms, a study has suggested.
Early research shows the infection is mild in four out of five cases, with young people in particular rarely becoming seriously ill.
Nevertheless, NHS doctors were told to look out for signs of "multi-system inflammation" after intensive care units in London saw eight children with unusual symptoms, some of whom tested positive for the coronavirus.
The inflammatory syndrome has been likened to atypical Kawasaki disease; a rare condition that usually affects children under five and causes blood vessels to become inflamed, leading to heart complications in around a quarter (25%) of patients. Left untreated, it can be fatal in 2% to 3% of cases.
Difficulty swallowing, swollen eyes and even brain damage have been flagged as symptoms.
Scientists from University College London (UCL) have now reported around half of the children admitted to hospital with the inflammatory syndrome have neurological symptoms, including impaired co-ordination, headaches and even hallucinations.
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"With this new inflammatory syndrome that develops after children are infected with the coronavirus, we are still learning how the syndrome affects children and what we need to watch out for," said study author Dr Omar Abdel-Mannan.
"We found many children experienced neurologic symptoms involving both the central and peripheral nervous systems."
The UCL scientists reviewed the records of all 46 children who "met the criteria" for multi-system inflammatory syndrome and were admitted to Great Ormond Street Hospital (GOSH) from 4 April to 1 September, 2020.
Results reveal 24 of the children (52%), average age 10, developed a newfound neurological symptom.
All 24 experienced headaches, while 14 also had encephalopathy; a general term for brain disease that alters the vital organ's function or structure.
Six developed voice abnormalities or hoarseness, symptoms that have previously been flagged with the coronavirus-inflammatory syndrome.
Six also endured hallucinations, while five had ataxia; disorders that affect co-ordination, balance and speech.
Three of the children developed "problems with their peripheral nerves", which lie in the brain and spinal cord. It is unclear what these problems involved.
One patient also endured seizures, the results – presented at the American Academy of Neurology's annual meeting – show.
Overall, the 24 children were more likely to require a ventilator and drugs that stabilise their blood circulation than those without the neurological symptoms.
Developing these symptoms was not linked to specific patient characteristics, like age.
It was also not associated with higher levels of inflammation; a key driver of coronavirus complications.
In addition, short-term outcomes did not differ between the children with and without the neurological symptoms.
"Children who develop this condition should definitely be evaluated for neurologic symptoms and longer- term cognitive outcomes," added Dr Abdel-Mannan.
"More studies are needed involving more children and following children to see how this condition changes over time and if there are any longer-term neurocognitive effects."
What we know about the coronavirus-inflammatory syndrome in children
The Royal College of Paediatrics and Child Health (RCPCH) has previously said "paediatric inflammatory multi-system syndrome temporally associated with coronavirus" can occur alongside or a few weeks after a positive or negative test for the infection, providing any other "microbial cause" is ruled out.
While cases of the inflammatory syndrome have spiked during the pandemic, not everyone with the condition swabs positive for the coronavirus, which may come down to a false-negative result.
Scientists from the New York University Grossman School of Medicine have previously noted "significant clinical overlap exists" between Kawasaki and the coronavirus-related inflammatory syndrome.
The latter, however, "has been characterised by more widespread systemic inflammation and higher rates of acute complications, including cardiogenic shock"; when the heart suddenly cannot pump enough blood to meet the body's needs.
The inflammatory disorder has also been likened to toxic shock syndrome (TSS).
Often associated with tampon use, TSS is a medical emergency that can lead to fever, flu-like symptoms, nausea, vomiting and difficulty breathing.
Experts have warned these symptoms are a sign the body is overwhelmed as it tries to fight an infection.
While the inflammatory syndrome may sound alarming, the vast majority of children are said to recover with hospital treatment, with experts repeatedly stressing there is no need to panic.
The RCPCH previously advised parents call 999 or take their child to A&E if they:
Become pale, mottled or abnormally cold to touch
Pause in their breathing, have an irregular breathing pattern or grunt
Have severe breathing difficulties, while becoming agitated or unresponsive
Go blue around the lips
Have a seizure
Become extremely distressed, confused, lethargic or unresponsive
Develop a rash that does not disappear with pressure, like when pressed under a glass
Have testicular pain, especially teenagers
GOSH has also flagged fatigue, red or cracked lips, swelling and peeling of the hands and feet, headaches, swollen lymph nodes in the neck, and unexplained irritability as symptoms of coronavirus-related inflammation.
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