A Case of Nephrotic Syndrome with Nephrotoxicity Induced by Low-Dose Cyclosporin Treatment

We report a 3-year-old girl with steroid resistant nephrotic syndrome (NS) who developed nephrotoxicity by low-dose cyclosporin (CsA) treatment. Initial prednisolone (PSL) treatment and subsequent additional cyclophosphamide treatment were not successful in leading her into remission. The first renal biopsy finding revealed neither a glomerular nor interstitial change. CsA therapy was initiated in addition to ongoing glucocorticoid therapy at 6 months from the time of onset. Proteinuria disappeared 3 weeks later and the patient went into complete remission. After experiencing the first relapse, the patient was gradually weaned from CsA, and treatment continued with 30 to 50 ng/mL of trough concentration. No elevations of the serum creatinine, serum urea, serum potassium, excretion of urinary β2-microglobulin, or urinary N-acetyl-βD-glucosaminidase were demonstrated in the follow-up. A second renal biopsy specimen obtained 1 year later showed a tubulo-interstitial change, containing tubular atrophy and interstitial fibrosis, both of which are consistent with the morphological change associated with CsA nephrotoxicity. A follow-up biopsy should be done in order to evaluate the CsA nephrotoxicity, regardless of the treatment dosage.