Seven consecutive paediatric patients with symptoms suggesting a long COVID, who were explored by 18F-FDG brain PET, were retrospectively included in our centre at Timone Hospital, Marseille, France, from August 20th, 2020 to November 17th, 2020. The clinical criteria of inclusion were the following: children under 18 years old, with an history compatible with SARS-CoV-2 infection, having had a medical evaluation 4 weeks or more after initial symptoms for functional complaints (persistent or recurrent fatigue, fever, chills, anorexia, weight loss, bulimia, dyspnoea, cough, headache, chest pain, musculoskeletal pain, diarrhoea, haematuria, dysmenorrhea, skin rash, dysautonomia such as palpitations and vagal hypotension, hyposmia/anosmia, dysgeusia/ageusia, cognitive impairment such as memory difficulties and concentration difficulties, hypersomnia, insomnia, stress, depression, visual impairments, decreases in scholastic achievement and limitation of extracurricular activities). During this inclusion period of less than 3 months, and given the weak data then available in the literature on long COVID, the aetiology of such clinical presentations was considered particularly uncertain. The PET exam was performed to investigate differential diagnosis and particularly possible encephalitis, whose presentation can be particularly atypical in children23. No other PET exam was performed in this context from November 17th, 2020 to the submission of the present article (except the control of two of the 7 children thereafter presented). Of note, our centre is a paediatric hospital with strong experience of brain 18F-FDG PET in this population.
Confirmed SARS-CoV-2 infection was defined by a positive biological result established by RT-PCR at the time of initial symptoms or by serology (ELISA or immune assay). Probable SARS-CoV-2 infection was defined by clinical features during the pandemic period (one or several of the following: fever, cough, dyspnoea, chest pain, pneumoniae, asthenia, headache, rhinitis, pharyngitis, muscular pain, diarrhoea, abdominal pain, hyposmia/anosmia, dysgeusia/ageusia). Contact with a confirmed case was searched for these patients.
We collected the clinical and paraclinical variables from the electronic patient record system (DPI aXigate®): age; sex; history of contact with a proven COVID-19 case before symptoms; day 0 of SARS-CoV-2 infection as defined by initial symptom onset; details of initial symptoms; initial level of C-reactive protein; initial clinical general status, described as asymptomatic, mild, moderate or severe according to Dong et al.24 and using NEWS score16; initial CT lung severity score (using 2 grades: normal/minimal vs. intermediate/severe involvement); co-infection; SARS-CoV2 RT-PCR; SARS-CoV2 serology; initial treatment (antibiotics, other); long-course treatment before acute COVID-19; possible differential diagnosis; and functional complaints more than 4 weeks after acute COVID-19.
At comparative purpose, we selected age-matched control patients (n = 20; mean age 12.7yrs ± 2.2) scanned under identical conditions from our database, in whom visual interpretation was normal and somatic cerebral diseases thereafter excluded at the follow-up. PET findings obtained between these two paediatric groups (long COVID and controls), were compared to those previously reported in adult long COVID and healthy subjects of our previous article16.
This data collection in adult and paediatric patients was retrospective, requiring no ethical approval after written inquiry and response from our institutional board (registration of the response on the following reference: PADS20-296). The patients and their parents or legal representatives received information and were not opposed to the use of their anonymized medical data in accordance with French and European regulations. This study respects the GPDR (General Data Protection Regulation) requirements.
Data in adult healthy subjects correspond to a previous interventional study registered in ClinicalTrials.gov with the following reference NCT00484523, and ethically approved by CPP Sud Mediterranée on the following reference 2007-A00180-53.
18 F-FDG PET imaging and processing
18F-FDG brain PET scans were acquired in the same centre using a same protocol, in subjects fasted for at least 4 hours with a controlled, normal glycaemia level, using an integrated PET/CT General Electric camera (Waukesha, WI), after intravenous administration of 111 MBq per 15-min acquisition at 30 min post-injection. Images were reconstructed on a 192×192 matrix using the ordered subsets expectation-maximization algorithm and corrected for attenuation using a CT transmission scan.
The SPM8 software (Wellcome Department of Cognitive Neurology, University College, London, UK) was used to proceed whole-brain voxel-based analysis. The four groups of subjects were implemented in a same ANOVA statistical model, with age and sex as nuisance covariables. In detail, the PET images were spatially normalized using the Montreal Neurological Institute (MNI) atlas. The dimensions of the resulting voxels were 2×2×2 mm. The images were smoothed with a Gaussian filter (8 mm full-width at half-maximum) to blur individual variations in the gyral anatomy and to increase the signal-to-noise ratio. Proportional scaling was performed to give the same global metabolic value to each PET examination. The SPM(T) PET maps were obtained at a height threshold (voxel-level significance) of p < 0.001, with a correction for multiple comparison at cluster-level using the family-wise error (FWE) rate for a p-cluster < 0.05. The whole-brain statistical comparison was first performed between paediatric patients with long COVID and paediatric controls, to search hypo- or hypermetabolism in patients. In case of no significant findings at this whole-brain correction level for one or more of the four regions previously identified as hypometabolic in adult patients with long Covid (olfactory gyrus, medial temporal lobe, brainstem, cerebellum), this approach was completed by a small volume correction on regions-of-interest defined on AAL atlas25 (p-voxel < 0.05 FWE-corrected). Finally, the comparison was done at whole-brain voxel-based level between the four groups of subjects to identify regions which were possibly more hypometabolic in adult patients than in paediatric patients with long COVID (in comparison to their respective controls groups), and those which were more hypometabolic in paediatric patients than in adult patients with long COVID (1–1 -1 1 and − 1 1 1–1 contrasts, considering the four groups on the following order: children with long COVID, paediatric controls, adults with long Covid, healthy adult subjects).