DMSA Scan: Purpose and Procedure
A DMSA (Tc-99m dimercaptosuccinic acid) renal scan is a nuclear medicine imaging study that evaluates renal cortical function and detects renal parenchymal abnormalities, particularly renal scarring and acute pyelonephritis, with superior sensitivity compared to ultrasound or CT. 1
Primary Clinical Purposes
Detection of Renal Scarring:
- DMSA scanning is the gold standard imaging modality for detecting renal parenchymal scarring, with ultrasound showing only 5.2% sensitivity for focal scarring compared to DMSA 2
- The scan identifies permanent cortical defects (reflux nephropathy) defined as defects in the renal outline or contraction of the whole kidney 3
- In children with vesicoureteral reflux (VUR), DMSA is recommended when renal ultrasound is abnormal, with breakthrough UTI, VUR grade III-V, or elevated serum creatinine 1
Acute Pyelonephritis Evaluation:
- DMSA is more sensitive than ultrasound for detecting acute pyelonephritis in pediatric populations, though it is not indicated for initial evaluation in uncomplicated adult pyelonephritis 1
- In children, DMSA helps differentiate lower urinary tract infection from pyelonephritis when clinical distinction is difficult 1
- Patients with abnormal DMSA scans during acute infection show longer febrile periods, higher positive culture rates, and increased renal insufficiency incidence 4
Differential Renal Function Assessment:
- The scan provides quantitative assessment of split renal function between kidneys 5
- Useful for monitoring renal growth and detecting functional abnormalities in children with recurrent UTIs 1
Timing Considerations
For Scarring Detection:
- NICE guidelines recommend DMSA scanning 4-6 months after atypical or recurrent infection in children <3 years, and for recurrent infection in children >3 years 1
- This delayed timing allows differentiation between transient acute changes and permanent scarring 3
- Lesions from acute pyelonephritis can completely heal or progress to permanent scarring, making early prediction impossible 3
During Acute Infection:
- When performed during febrile UTI, DMSA identifies children at risk for developing renal scars, though outcome cannot be predicted 3
- In adults with acute pyelonephritis, 46% show DMSA abnormalities, with 75% of focal/multifocal defects resolving by 6 months 6
Clinical Limitations and Pitfalls
Not First-Line in Adults:
- DMSA is not indicated for initial evaluation of uncomplicated acute pyelonephritis in adults, as CT is more accurate for detecting involvement 1
- CT shows significantly higher sensitivity than DMSA for acute pyelonephritis in adult patients 1
Interpretation Challenges:
- Acute pyelonephritis causes transient abnormalities that can occur in normal or previously scarred kidneys 3
- DMSA may underestimate degree of renal involvement compared to MR urography in children with VUR and pyelonephritis history 1
- Pitfalls include tubular dysfunction, hypertension, captopril use in renovascular hypertension, and duplex kidneys 3
Pediatric-Specific Role:
- The evidence supporting DMSA use is generally older than that for alternative modalities like voiding urosonography and VCUG 1
- A normal DMSA in children with recurrent infections may exclude high-grade reflux, potentially avoiding invasive VCUG 1
Procedure Overview
The scan uses Tc-99m-labeled dimercaptosuccinic acid, which binds to functioning renal cortical tissue 1. The radiotracer accumulates in proximal tubular cells, allowing visualization of functional renal parenchyma and identification of cortical defects 6, 3. Quantitative assessment includes renal area involvement and split function calculations 5.