Rabson-Mendenhall syndrome: medullary sponge kidney, a new component.

Rabson-Mendenhall syndrome is a rare genetic disorder characterized by severe insulin resistance, extreme hyperinsulinemia, postprandial hyperglycemia, growth retardation, and dysmorphisms. Enlargement of the kidneys and nephrocalcinosis have been described previously. We report a 10-year-old boy who presented with gross hematuria, unilateral hydronephrosis, and the initial diagnosis of bilateral extensive medullary nephrocalcinosis. Medullary sponge kidney (MSK) was included in the differential diagnosis given the ultrasound findings. Further evaluation by intravenous pyelogram confirmed the suspected bilateral MSK. Given the patient's history of hydronephrosis due to an obstructing renal stone and MSK, urine calcium excretion was assessed and found to be markedly increased at 9.5 mg/kg per day. To our knowledge, this is the first report of Rabson-Mendenhall syndrome and an association with MSK. We recommend evaluation for nephrocalcinosis, MSK, and hypercalciuria in all children diagnosed with Rabson-Mendenhall syndrome.