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Pediatr Nephrol (2012) 27:225227 DOI 10.1007/s00467-011-1914-x
CLINICAL QUIZ
An unusual DMSA scan: answer
Alison Timmis & Caroline Jones & Fauzia Paize
Received: 10 November 2010 /Revised: 28 April 2011 /Accepted: 29 April 2011 /Published online: 8 June 2011 # IPNA 2011
Keywords Paediatric . Urinary tract infection . DMSA scan .
Tubulopathy
Answer: Tubulopathy secondary to Dent disease.
Case summary
A further renal ultrasound scan at the age of 6 years showed nephrocalcinosis. In view of the proteinuria, the patient was started on enalapril. The family had previously refused the use of oral citrate or a thiazide as they viewed the child to be asymptomatic but were prepared to introduce a no-added-salt diet and encourage adequate fluid intake. The use of oral citrate was considered unpalatable and they were reluctant to introduce a thiazide because of the potential side-effects and that there was no guarantee of improved clinical outcome. Subsequent genetic analysis has revealed a mutation p.Gly57Arg in the CLCN5 gene confirming the diagnosis. This mutation has not been described before, but is felt to be pathogenic, as pGly57Val has previously been identified as a pathogenic mutation [1].
Discussion
Technetium-99 m-dimercaptosuccinic acid (99mTc-DMSA) and Technetium-99 m mercaptoacetyltriglycine (99mTc-
MAG3) are both radioisotope agents that can be utilized in renal scintigraphy in conjugation with a gamma camera.
99mTc-DMSA is a renal cortical imaging agent. Static renal scintigraphy using 99mTc-DMSA obtains information about the overall morphology of the functional renal unit, split renal function, and detects parenchymal abnormalities. It is a highly useful imaging technique for identifying a renal cortical scarring or defect. 99mTc-DMSA is a dithiol and localizes to the renal cortex by binding to sulfhydryl groups in the proximal tubules [2].
Renal uptake of 99mTc-DMSA approximates to the functional renal cortical mass, which depends on renal blood flow and proximal tubular membrane transport function. Renal scintigraphy using 99mTc-MAG3 is a dynamic scan. It allows simultaneous investigation of renal perfusion and the presence of any obstruction.
In order for there to have been a complete absence of uptake of 99mTc-DMSA despite a normal 99mTc-MAG3, there must be a defect in the transport mechanism into the proximal tubular cells of 99mTc-DMSA in this child. This DMSA abnormality led to the early diagnosis of Dent disease in this...