Decreased stone-free rates after percutaneous nephrolithotomy for high calcium phosphate composition kidney stones

To our knowledge the most effective treatment in patients with renal stones containing calcium phosphate remains unknown. An inverse correlation exists between calcium phosphate stone composition and the stone-free rate of shock wave lithotripsy. It is unknown whether this is due to treatment type (shock wave lithotripsy) or to a feature unique to calcium phosphate stones. We determined whether calcium phosphate stone composition affects the stone-free rate of percutaneous nephrolithotomy.

Percutaneous nephrolithotomy was performed in 111 patients between 2001 and 2006 and stone fragments were analyzed for calcium phosphate composition. Patients were categorized into groups based on calcium phosphate content. All patients underwent preoperative computerized tomography. Patients were considered stone-free after percutaneous nephrolithotomy when fragments were 2 mm or less on noncontrast computerized tomography.

A total of 213 percutaneous nephrolithotomies were performed. An increased percent of calcium phosphate was related to a decreased percutaneous nephrolithotomy success rate (p = 0.005), independent of preoperative stone burden (p = 0.8). Patients with greater than 60% calcium phosphate stones were significantly less likely to be stone-free after percutaneous nephrolithotomy than those with less calcium phosphate (60%, OR 2.45, 95% CI 1.103-5.4401 vs 80%, OR 3.72, 95% CI 1.33-10.44).

High calcium phosphate renal stone content leads to a decreased stone-free rate. Further study is required to determine the mechanism of stone resilience as well as the most appropriate treatment modality in patients with high calcium phosphate composition kidney stones.