Abstract
Ammonium acid urate (AAU) crystals in urine sediment have recently started to attract attention for the possibility of calculus formation. Here, we report on our experience of treating four pediatric cases of nephrotic syndrome (NS) with AAU crystals in urine sediment. The patients, who were all boys aged 1, 4, 7, and 11 years, were hospitalized for edema and severe proteinuria. They were discharged after achieving remission with steroid therapy. In all the four patients, concentrated urine with high urine specific gravity and low urine output was noted. AAU crystals were detected in the urine only once or twice during the hospitalization. In one of the patients, AAU calculi stuck at the balloon catheter tip were noted on the same day as when the patient was admitted. Many of the mechanisms of calculus formation are unknown. In cases of pediatric NS, however, severe dehydration and urine concentration were considered to develop even without diarrhea or vomiting observed in rotavirus enterocolitis and lead to AAU crystal formation. Crystals in the urine, which indicate the saturation of components, are an important finding indicative of a risk of the onset of acute postrenal failure caused by AAU calculi in pediatric NS. In all of the cases, AAU crystals appeared during the period of severe NS. However, the longitudinal data on protein concentration, specific gravity, and volume of urine suggest that the crystals tended to appear immediately before the recovery from the disease.
