Acute interstitial nephritis predisposed a six-year-old girl to minimal change nephrotic syndrome

A six-year-old girl was admitted to our hospital with acute renal failure. We made a clinical diagnosis of acute interstitial nephritis and oral corticosteroid therapy was started. Her renal failure soon recovered, and renal biopsy showed acute interstitial nephritis by light microscopy with glomerular foot process effacement by electron microscopy. Although her proteinuria was not heavy at the time of biopsy, her proteinuria subsequently increased to show nephrotic syndrome. We continued to give corticosteroids and her nephrotic syndrome went into remission 13 days after biopsy. Serological and bacteriological examination showed no evidence of known pathogen or drug hypersensitivity. The time changes in proteinuria were monitored by fractional total protein excretion (FETP) and fractional β2 microglobulin excretion (FEβ2MG) in order to evaluate the severity of proteinuria under different glomerular filtration rates and different proximal tubular functions. The results revealed that nephrotic syndrome had occurred during recovery from acute interstitial nephritis. This is the first case report to show the sequential occurrence of acute interstitial nephritis and nephrotic syndrome based on evidence from fractional protein excretion.