3D MRI predicts course of polycystic kidney disease

Volumetric MR scanning can accurately track structural changes preceding the onset of autosomal dominant polycystic kidney disease, according to a study by the National Institute of Diabetes and Digestive and Kidney Diseases. MR could sound the alarm on disease progression earlier than standard blood and urine tests.

As many as a half-million people in the U.S. have polycystic kidney disease (PKD), which is genetically transmitted. Patients develop multiple cysts that severely affect their renal and liver function. They also suffer from high blood pressure and brain aneurysms. Until now, physicians had to observe PKD patients for years before they could tell if a treatment worked.

MRI can spot structural changes that correlate with PKD-related kidney dysfunction and track the factors that contribute to development of the disease. An accurate prediction of disease progression should speed up trials of potential therapies, said principal investigator Dr. Jared J. Grantham, a kidney specialist at the University of Kansas School of Medicine in Kansas City.

"It should now be possible to test potential therapies earlier in the disease, when therapies are more likely to prevent kidney failure," Grantham said.

Grantham and colleagues from the Consortium for Radiological Imaging Studies of Polycystic Kidney Disease (CRISP) enrolled 241 patients with autosomal dominant PKD and normal to mildly impaired kidney function. They used a 3D MRI technique to measure these patients' kidneys, their cysts, and the proportion of renal tissue occupied by the cysts. They compared changes in cyst and kidney volume to standard blood/urine tests and a specialized kidney function test.

MRI data showed that, albeit distinctively in each individual PKD case, cysts large and small grew almost simultaneously and at steady rates in both kidneys and regardless of patient age (NEJM 2006;354[20]:2122-2130).

The researchers used coronal T2-weighted and gadolinium-enhanced 3D volume-interpolated, spoiled gradient-echo coronal T1-weighted images with a slice thickness of 3 mm. MR scans determined that total kidney volume at baseline among 214 patients was about 1100 mL, which increased by more than 200 mL over a three-year period. The total cyst volume among 210 patients during the same period increased by more than 218 mL.

The baseline total kidney volume predicted the subsequent rate of increase in volume, independently of age. A baseline total kidney volume above 1500 mL in 51 patients was associated with a declining glomerular filtration rate (4.33±8.07 mL/min/year). All correlations were statistically significant (p<0.001).

Because of wide variability in kidney function loss among PKD patients - even within families with the same altered gene - physicians assumed that cysts and kidneys would grow at variable rates. It was thus quite remarkable to find cysts and kidneys in individuals growing at uniform and predictable rates, said Dr. Catherine M. Meyers, a National Institute of Diabetes and Digestive and Kidney Diseases kidney specialist.

"Our experience is still limited, but this method appears very promising," Meyers said.

Some of these patients will undergo another four years of MRI monitoring. About 100 of them could join the National Institute's HALT-PKD trial, the first to use CRISP's MRI method along with standard tests of kidney function. The HALT-PKD trial enrolled its first patient in January.

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