RENAL CORTICAL SCINTIGRAPHY IN THE DIAGNOSIS OF ACUTE PYELONEPHRITIS

Comparative clinical studies have shown renal cortical scintigraphy, using technetium-99m (99mTc)-labeled glucoheptonate or dimercaptosuccinic acid (DMSA), to be significantly more sensitive than either intravenous pyelography or renal sonography in the diagnosis of acute pyelonephritis. However, due to uncertainties about the diagnostic accuracy of the clinical and laboratory parameters used in these studies, true sensitivity of renal cortical scintigraphy was unknown. Therefore, we evaluated the accuracy of [99mTc]DMSA scintigraphy in the diagnosis of experimentally induced acute pyelonephritis in piglets using strict histopathologic criteria as the standard of reference. The sensitivity and specificity of the DMSA scan for the diagnosis of acute pyelonephritis were 91% and 99%, respectively, with an overall 97% agreement between the scintigraphic and histopathologic findings. Based on the results of this experimental study, we used the [99mTc]DMSA scan as the standard of reference for the diagnosis of acute pyelonephritis, and conducted a prospective clinical study of 94 children hospitalized with the diagnosis of acute febrile urinary tract infection (UTI). The aims of this study were (1) to determine the relationship among vesicoureteral reflux, P-fimbriated Escherichia coli, acute pyelonephritis, and renal scarring, and (2) to evaluate the diagnostic reliability of the clinical and laboratory parameters commonly used in the diagnosis of acute pyelonephritis. We documented acute pyelonephritis in 62 (66%) of 94 patients. Vesicoureteral reflux was demonstrated in 29 (31%) of the total group and in only 23 (37%) of 62 patients with acute pyelonephritis. The prevalence of P-fimbriae in the E coli isolates was 64% in the patients with acute pyelonephritis and 78% in those with a normal DMSA scan. Even in patients without reflux, P-fimbriae were found in 71% of isolates from the patients with acute pyelonephritis and in 75% of those with a normal renal scan. Follow-up DMSA scans were obtained in 33 patients with acute pyelonephritis in 38 kidneys. We found complete resolution of the acute inflammatory changes in 58% of the involved kidneys and renal scarring in the remaining 42%, including 40% of the kidneys associated with reflux and 43% of those without reflux. The results of these experimental and clinical studies show the following: (1)[99mTc]DMSA renal cortical scintigraphy is a highly sensitive and reliable technique for the diagnosis of acute pyelonephritis; (2) the diagnosis of acute pyelonephritis in children based on clinical and laboratory observations is unreliable; (3) acute pyelonephritis in the absence of reflux is common; (4) the presence of P-fimbriae alone does not fully explain the pathogenesis of acute pyelonephritis in the absence of reflux; (5) although high grades of reflux may be a risk factor for acute pyelonephritis, the risk of pyelonephritis in patients with lower grades of reflux is the same as in those with no reflux; and (6) once acute pyelonephritis occurs, subsequent renal scarring is independent of the presence or absence of reflux. We conclude that DMSA renal cortical scintigraphy is a valuable diagnostic tool for investigating UTI, particularly in children. More precise diagnosis of acute pyelonephritis allows for newer insights into the pathophysiology of the disease and prevention of its sequelae, and in the future it may change the approach to the imaging evaluation and management of children with UTI. © 1991 W.B. Saunders Company. All rights reserved.