Multicentric Castleman disease is a rare lymphoproliferative disorder of unknown cause in children. Renal involvement of Castleman disease is uncommon. Proteinuria in association with multicentric Castleman disease has been reported to occur infrequently in only adult patients. We report a 12-year-old boy that presented with recurrent abdominal pain, diarrhea, anemia, high sedimentation rate (ESR) and fibrinogen level. He was suspected to have familial Mediterranean fever (FMF) and treated with colchicine. Unfortunately, he showed no marked improvement in the clinical and laboratory findings. Despite a comprehensive evaluation, his diagnosis remained elusive for several years. Eventually, three years later, he was found to have 42 gr/day of proteinuria. Renal biopsy was reported as normal. During the laboratory work-up for the etiology of proteinuria, an intraabdominal mass sized 5x4cm was found by abdominal ultrasonography. The patient’s clinical and laboratory findings such as anemia, pergamaglobulinemi, increased ESR and excessive proteinuria led us to think the diagnosis of Castleman disease. He underwent to the surgery with the presumptive diagnosis of Castleman disease. Pathologic examination was confirmed as Castleman disease mixed type. After removal of the mass, one month later, all the abnormal laboratory findings including anemia, excessive proteinuria, and increased ESH, fibrinogen and immunoglobulin levels disappeared. In this case, the proteinuria appears to be related to Castleman disease and removal of the mass relieved proteinuria. To our knowledge, this interesting case is the first report of the occurrence of proteinuria in a in a child with Castleman disease

Keywords: Multicentric Castleman disease, proteinuria, children, renal involvement, angiofollicular, lymph node hyperplasia