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Hemolytic uremic syndrome (HUS) is often encountered in children with acute kidney injury. Besides the well-known shiga toxin-producing Escherichia coli-associated HUS, atypical HUS (aHUS) caused by genetic complement dysregulation has been studied recently. aHUS is a rare, chronic, and devastating disorder that progressively damages systemic organs, resulting in stroke, end-stage renal disease, and death. The traditional treatment for aHUS is mainly plasmapheresis or plasma infusion; however, many children with aHUS will progress to chronic kidney disease despite plasma therapy. Eculizumab is a newly developed biologic that blocks the terminal complement pathway and has been successfully used in the treatment of aHUS. Currently, several guidelines for aHUS, including the Korean guideline, recommend eculizumab as the first-line therapy in children with aHUS. Moreover, life-long eculizumab therapy is generally recommended. Further studies on discontinuation of eculizumab are needed.

Idiopathic nephrotic syndrome (INS) in children is characterized by massive proteinuria and hypoalbuminemia. Minimal change nephrotic syndrome (MCNS) is the most common form of INS in children. The pathogenesis of MCNS still remains unclear, however, several hypotheses have been recently proposed. For several decades, MCNS has been considered a T-cell disorder, which causes the impairment of the glomerular filtration barrier with the release of different circulating factors. Increased levels of several cytokines are also suggested. Recently, a "two-hit" theory was proposed that included the induction of CD80 (B7-1) and regulatory T-cell (Treg) dysfunction, with or without impaired autoregulatory functions of the podocyte. In contrast to the well-established involvement of T cells, the role of B cells has not been clearly identified. However, B-cell biology has recently gained more attention, because rituximab (a monoclonal antibody directed against CD20-bearing cells) demonstrated a very good therapeutic response in the treatment of childhood and adult MCNS. Here, we discuss recent insights into the pathogenesis of MCNS in children.

Drug rash with eosinophilia and systemic symptoms (DRESS) syndrome is a rare and potentially fatal condition characterized by skin rash, fever, eosinophilia, and multiorgan involvement. Various drugs may be associated with this syndrome including carbamazepine, allopurinol, and sulfasalazine. Renal involvement in DRESS syndrome most commonly presents as acute kidney injury due to interstitial nephritis. An 11-year-old boy was referred to the Children's Hospital of Pusan National University because of persistent fever, rash, abdominal distension, generalized edema, lymphadenopathy, and eosinophilia. He previously received vancomycin and ceftriaxone for 10 days at another hospital. He developed acute kidney injury with nephrotic range proteinuria and hypocomplementemia. A subsequent renal biopsy indicated the presence of acute tubular necrosis (ATN) and late exudative phase of postinfectious glomerulonephritis (PIGN). Systemic symptoms and renal function improved with corticosteroid therapy after the discontinuation of vancomycin. Here, we describe a biopsy-proven case of severe ATN that manifested as a part of vancomycin-induced DRESS syndrome with coincident PIGN. It is important for clinicians to be aware of this syndrome due to its severity and potentially fatal nature.

Paraneoplastic limbic encephalitis, a remote effect of cancer without nervous system metastasis, is rare, especially in childhood. Here, we report a case of paraneoplastic limbic encephalitis associated with an ovarian mature teratoma in an adolescent girl. The 15-year-old girl developed neuropsychiatric symptoms, memory loss, seizures, and unconsciousness. Cerebrospinal fluid analysis and brain magnetic resonance imaging (MRI) findings were normal, while single photon emission computed tomography imaging showed hypoperfusion in both temporal lobes. Ultrasound and MRI of the abdomen revealed a left ovarian cystic mass. The patient experienced a significant recovery of cognitive function after surgical resection of the tumor, which was pathologically identified as a mature ovarian teratoma, and treatment with intravenous immunoglobulin.