New treatment strategies in idiopathic nephrotic syndrome

Idiopathic nephrotic syndrome (INS) is probably due to a plasma factor of immunologic origin. This circulating factor probably interacts with the glomerular filtration barrier and is responsible for massive proteinuria. Most patients respond to steroids. However, a considerable proportion of children run a steroid dependent course. Cyclosporine A (CyA) and cyclophosphamide (CyP) have been classical treatment strategies for such cases, but specific toxicity limits the use of these drugs. Mycophenolate mofetil (MMF), an inhibitor of inosine monophosphate dehydrogenase and thus de novo purine synthesis. Clinical trials have demonstrated the efficacy of MMF in steroid dependent NS and in children with nephrotoxicity due to prolonged CyA treatment. While MMF is a well established strategy against steroid dependency, rituximab (RTX) has emerged as a new treatment option in case of calcineurin inhibitor dependency. Non-compliance to steroid therapy can be responsible for multiple relapses and may be misinterpreted as steroid dependency and may therefore lead to unjustified increase of the immunosuppressive treatment. Triamcinolone acetonide, a long acting steroid for intramuscular injection, can replace the usual oral prednisone treatment if non-compliance is suspected. Whereas the treatment of the primary course of INS is well established, steroid dependent and steroid resistant forms are still a challenge for pediatric nephrologists. Both under-treatment with multiple relapses with disease or steroid associated morbidity on the one hand and over-treatment with specific side effects of immunosuppressive drugs may have severe consequences for the patients. The narrow path between steroid side effects and potential nephrotoxicity emphasizes the need for individualized management in severe form of INS.