Decreased concentrating capacity in children with febrile urinary tract infection and normal 99mTc-dimercaptosuccinic acid scan: does medullonephritis exist?

Background: Although 99mTc-dimercaptosuccinic acid (DMSA) scan is considered the gold standard for the diagnosis of acute pyelonephritis (AP), sometimes it produces false results in children with clinical features of AP. There are no studies on the comparison of the sensitivity of DMSA and concentrating capacity test. Methods: Eighty-five infants with AP of less than one year old were studied to evaluate whether they had real AP or not. Data were compared between infants with an abnormal (group A, n=64) and those with a normal DMSA scan (group B, n=21) respectively. A DDAVP test was performed for each infant. Results: All the infants in both groups presented a high level of C-reactive protein and fever (>38 degrees C). There were no differences in clinical and analytical variables except C-reactive protein level in the two groups. Both groups exhibited a low urinary osmolality (87.5% in the group A vs. 85.7% in the group B). The patients with normal DMSA and decreased concentrating capacity have some renal parenchymal damage and not only a lower urinary infection. Of the infants with an abnormal DMSA scan, 33.9% showed renal scars after 6-12 months. No infant with a normal DMSA scan showed scars. The biochemical variables in both groups of infants were not related to vesicoureteral reflux. Conclusion: Infants with AP, normal DMSA scan and low concentrating capacity may be characterized by a localized infection in the medulla (medullonephritis) or by a false negative DMSA scan.