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Imaging after urinary tract infection reconsidered

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Researchers in three US centres (Pittsburgh, Pennsylvania; Columbus, Ohio; and Boston, Massachusetts) have offered a minimalist view of the necessity for imaging studies after urinary infection in young children (

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They studied 309 children aged 1 to 24 months with a first febrile urinary tract infection (10 or more white cells per cubic millimeter in uncentrifuged urine, 1 or more gram-negative rods per 10 oil-immersion fields, and 50000 or more colony forming units of a single pathogen from a catheter specimen). All 309 children had a renal ultrasound scan and a technetium-99m-labelled dimercaptosuccinic acid (DMSA) scintigram within 48 hours of diagnosis, 302 had a voiding cystourethrogram after 1 month and 275 had repeat DMSA scan and voiding cystourethrogram at 6 months.

The ultrasound scan was abnormal in 37 children (12%) but the abnormalities found were not considered to have affected treatment. Urinary tract obstruction was not found. (The authors of this paper attribute this to the use of antenatal ultrasound scanning but give no details of such scanning in their study population.) They recommend that ultrasound scanning should not be performed after a first urinary tract infection in children who have had an antenatal scan after 30 weeks gestation. The initial DMSA scans gave findings compatible with acute pyelonephritis in 190 children (61%). Only one child had a renal scar at that time. No child with a normal first DMSA scan had an abnormal follow up scan at 6 months. Twenty-six (15%) of 173 children with appearances of acute pyelonephritis on the first scan had renal scarring on the second but the extent of renal parenchymal involvement was small. These authors conclude that DMSA scanning is of limited value since it is unclear how the findings should influence treatment. They prefer to emphasise the importance of accurate diagnosis of urinary infection in subsequent febrile illnesses on follow up after a first urinary infection.

Voiding cystourography at 1 month showed vesicoureteric reflux in 117/302 children (39%). Fresh renal scarring occurred in 16/109 (15%) with reflux and 10/166 (6%) without. These authors point out that detecting reflux is only beneficial if prophylactic antimicrobial treatment prevents disease progression and that is unproved. (Their conclusion illustrates the ambiguity that can result from use of the passive voice. They state that “the use of voiding cystourethrography is recommended” but do not make it clear whether it is recommended by themselves or by others.)

They are against the routine use of ultrasound scans. They probably favour the use of voiding cystourethrography but qualify this approval with a call for further studies of the usefulness of prophylactic antimicrobial treatment. They suggest that a single DMSA scan is not useful and repeated DMSA scanning could probably be avoided by paying strict attention to the diagnosis and treatment of repeat urinary tract infections. The debate, which seems to have been going on forever, is obviously far from over.

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