NHS officials issued a high-priority alert to GPs at the end of April after a small number of cases of severe illness in young children amid concerns over a link with coronavirus.
Research led by the Imperial College Academic Health Science Centre (AHSC) has now confirmed that the inflammatory syndrome is a new condition - and that its emergence in many countries around the world during the COVID-19 pandemic suggests that 'a link with Sars-CoV-2 is likely'.
To date, less than 200 cases of the illness are thought to have been reported in England. Although most cases have recovered, the illness has been linked to potential 'long-lasting coronary damage' - and researchers warned that Black, Asian and Minority Ethnic (BAME) patients appear to be at increased risk.
The researchers have named the illness PIMS-TS - short for paediatric inflammatory multisystem syndrome temporally associated with SARS-CoV-2.
Cases of hospitalised children assessed by the researchers revealed 'three patterns of disease among children hospitalised with PIMS-TS', a paper published in the Journal of the American Medical Association (JAMA) shows.
One group had 'persistent fever and elevated levels of inflammatory markers, but without features of Kawasaki disease (KD), shock, or organ failure'. A second group 'fulfilled the diagnostic criteria for KD', the researchers found. A third group 'had shock and clinical, echocardiographic, and laboratory evidence of myocardial injury'.
The researchers reported wide variation in signs and symptoms among 58 hospitalised children assessed - with cases involving fever, gastrointestinal symptoms or rash, and variation in severity of disease, 'including myocardial injury, shock, and development of coronary artery aneurysms'. Comparison with patients cases of KD, KD shock syndrome and toxic shock syndrome 'suggests that PIMS-TS differs from these pediatric inflammatory entities', the researchers reported.
Of the 58 cases considered by the researchers, 45 'had evidence of current or prior Sars-CoV-2 infection', the researchers found - although not all patients received antibody tests. Of 46 patients who took antibody tests, 87% tested positive.
The researchers found that while KD appears to affect patients with an average age of around 4 years, PIMS-TS seems more likely among slightly older children, with an average age of 9 years, presenting 'more often with abdominal pains and diarrhoea alongside the common features such as persistent fever'.
The research found that blood tests on PIMS-TS patients revealed 'more markers of inflammation and cardiac enzymes' than tests on patients with KD, 'which suggest the heart is under strain'.
Dr Julia Kenny, consultant in paediatric infectious diseases and immunology at Evelina London, said: 'Our analysis has shown that this is indeed a new condition. Untreated, there is a risk of severe complications in very unwell children, but with early identification and treatment the outcome is excellent, with the children we are reviewing after discharge completely well.
'For clinicians, it’s important that we build collaborative research to quickly improve our understanding of the condition and provide the best evidence-based treatment for our patients.'
Lead researcher Professor Michael Levin, from the Department of Infectious Disease at Imperial College London, said: 'The new disease presents in a number of ways and can have serious complications. However, the more we learn the better prepared we are to intervene and prevent worse outcomes. For example, patients who develop shock and cardiac failure have a different pattern of blood tests that may help to identify the at-risk group for targeted treatment.'
The Royal College of Paediatrics and Child Health (RCPCH) published advice for GPs on how to spot cases of the illness in early May - warning that children could present with 'persistent fever, inflammation (neutrophilia, elevated CRP and lymphopaenia) and evidence of single or multi-organ dysfunction (shock, cardiac, respiratory, renal, gastrointestinal or neurological disorder) with additional features' that may include children 'fulfilling full or partial criteria for Kawasaki disease'.
The RCPCH has also produced advice for patients concerned about PIMS-TS.