Acute Kidney Injury in Multisystem Inflammatory Syndrome in Children (MIS-C).

Dear Editor,

We have read with great interest the manuscript entitled “Acute Kidney Injury in Multisystem Inflammatory Syndrome in Children (MIS-C): a Case Report” [1].

The authors present a 15-year-old girl who had been diagnosed with acute kidney injury (AKI) due to multisystem inflammatory syndrome in children (MIS-C). We have some concerns about the differential diagnosis of acute kidney injury in this patient. Firstly, urine examination which is a crucial step in the diagnosis of AKI is not mentioned in the text [2]. The existence of hematuria or proteinuria and the density of urine could all be helpful clues for the underlying cause of AKI [2].

The clinical picture described here represents a rapidly progressing course of AKI and a huge number of underlying causes may be responsible for this. Although the patient was dehydrated rather than overhydrated and this might be a clue for prerenal AKI, the possible underlying causes may be more comprehensively discussed before attributing the course to COVID-19. The ultrasonographic findings of this patient were not mentioned in the text. Without urine examination and ultrasound, one cannot complete the diagnostic work-up of AKI. Also, in rapidly progressive courses, renal biopsy should be part of diagnostic investigations.

Authors mention the rapid improvement of patient with intravenous immunoglobulin and one dose of bolus methyl prednisolone. A variety of AKI causes may respond to steroids or immune globulin as described in rapidly progressive glomerulonephritis, tubulointerstitial nephritis, and vasculitis-related glomerulonephritis.

We also want to emphasize that renal involvement has been reported too rarely, even not reported in several MIS-C series [3-6]. We are not sure how reliable it would be to suggest that an extremely rarely reported entity is caused by MIS-C before all possible diagnoses have been ruled out.

Due to the pandemic we are in, the focus of physicians on COVID-19 infection may lead to overdiagnosis of MIS-C. The suppression of inflammation, which can occur for many different reasons, by the IVIG, steroid, and immunomodulatory agents used in the MIS-C treatment, may lead to delay of the correct diagnosis. Therefore, we thought that it is very important to perform the diagnostic study for possible differential diagnosis of MIS-C before starting treatment for MIS-C.