Kidney Biopsy in Autosomal Dominant Polycystic Kidney Disease

Abstract

Proteinuria is an easily quantified biomarker of kidney disease and often a sign of glomerular pathology. Significant proteinuria is uncommon in cystic kidney diseases and should be further evaluated to exclude the presence of another simultaneous kidney disease. While renal biopsy is a valuable part of the diagnostic evaluation of proteinuria, careful consideration of risks and benefits is necessary before proceeding in a patient with bilateral renal cysts. We report the case of a man with Polycystic Kidney Disease (PKD) who was found to have nephrotic-range proteinuria. An ultrasound-guided kidney biopsy revealed evidence of Focal Segmental Glomerulosclerosis (FSGS), which was attributed to hyperfiltration-related injury in the context of extensive kidney cysts. Genetic testing did not reveal a cause of FSGS and showed a variant of uncertain significance in PKD1. We use this case to highlight three important issues that are applicable to patients with PKD: the role of diagnostic evaluation for proteinuria in cystic kidney disease, the feasibility of kidney biopsy despite the presence of bilateral renal cysts, and the roles and limitations of genetic testing in cystic kidney disease and FSGS.