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Published on: June 23, 2015
Expanded Imaging Classification of Autosomal Dominant Polycystic Kidney Disease
Kyongtae T Bae1, Tiange Shi2, Cheng Tao3
1Department of Radiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania baek@upmc.edu.
Insights
Recalculating kidney volume in autosomal dominant polycystic kidney disease (ADPKD) improves risk prediction for patients with atypical cyst morphology. This adjusted measurement enhances the accuracy of the Mayo classification for disease progression.
Area of Science:
- Nephrology
- Medical Imaging
- Genetics
Background:
- Autosomal dominant polycystic kidney disease (ADPKD) risk stratification relies on the Mayo Clinic imaging classification, utilizing height-adjusted total kidney volume (htTKV) and age.
- This classification is limited to patients with typical diffuse cystic disease (class 1) and poorly predicts kidney function decline in the 5%-10% of patients with atypical morphology (class 2).
Purpose of the Study:
- To refine the Mayo Clinic imaging classification for ADPKD by developing a more accurate risk prediction model for patients with atypical morphology.
- To assess the impact of excluding exophytic cysts from htTKV measurements on predicting chronic kidney disease (CKD) stage 3 and estimated glomerular filtration rate (eGFR) trajectory.
Main Methods:
- Identified patients with ADPKD from the HALT-A study, including class 2A with prominent exophytic cysts (class 2Ae) and class 1 with prominent exophytic cysts.
- Recalculated htTKVs for these patients, excluding exophytic cysts, and compared prediction accuracy for CKD stage 3 and eGFR trajectory using original and recalculated htTKVs in logistic and mixed linear models.
Main Results:
- Recalculated htTKVs increased specificity for developing CKD stage 3 from 82.6% to 84.2% across all participants.
- The prediction of CKD stage 3 in class 2Ae patients was better calibrated using recalculated htTKVs (45.5% predicted vs. 13.0% observed) compared to original htTKVs (63.6% predicted).
- Recalculated htTKVs significantly reduced the mean paired difference between predicted and observed eGFR for both class 2Ae (from 17.6 to 4.0 ml/min/1.73 m² ) and class 1 (from -1.7 to 0.1 ml/min/1.73 m²).
Conclusions:
- Excluding prominent exophytic cysts from htTKV measurements improves the accuracy of the Mayo classification for ADPKD.
- This adjusted htTKV measure facilitates the inclusion of class 2 patients and reclassification of class 1 patients, enhancing risk stratification for disease progression.
Background:
The Mayo Clinic imaging classification of autosomal dominant polycystic kidney disease (ADPKD) uses height-adjusted total kidney volume (htTKV) and age to identify patients at highest risk for disease progression. However, this classification applies only to patients with typical diffuse cystic disease (class 1). Because htTKV poorly predicts eGFR decline for the 5%-10% of patients with atypical morphology (class 2), imaging-based risk modeling remains unresolved.
Methods:
Of 558 adults with ADPKD in the HALT-A study, we identified 25 patients of class 2A with prominent exophytic cysts (class 2Ae) and 43 patients of class 1 with prominent exophytic cysts; we recalculated their htTKVs to exclude exophytic cysts. Using original and recalculated htTKVs in association with imaging classification in logistic and mixed linear models, we compared predictions for developing CKD stage 3 and for eGFR trajectory.
Results:
Using recalculated htTKVs increased specificity for developing CKD stage 3 in all participants from 82.6% to 84.2% after adjustment for baseline age, eGFR, BMI, sex, and race. The predicted proportion of class 2Ae patients developing CKD stage 3 using a cutoff of 0.5 for predicting case status was better calibrated to the observed value of 13.0% with recalculated htTKVs (45.5%) versus original htTKVs (63.6%). Using recalculated htTKVs reduced the mean paired difference between predicted and observed eGFR from 17.6 (using original htTKVs) to 4.0 ml/min per 1.73 m2 for class 2Ae, and from -1.7 (using original htTKVs) to 0.1 ml/min per 1.73 m2 for class 1.
Conclusions:
Use of a recalculated htTKV measure that excludes prominent exophytic cysts facilitates inclusion of class 2 patients and reclassification of class 1 patients in the Mayo classification model.
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