Purpose

Uric acid calculi with or without a calcium component comprise a significant proportion of urinary stones. Knowledge of the pathophysiology of stone formation is important to direct medical treatment. The aim of this review is to provide an update on the epidemiology, pathophysiology and management of uric acid renal stones.

Materials and methods

A MEDLINE search was performed on the topic of uric acid stones. Current literature was reviewed with regard to the epidemiology, pathophysiology, associated medical conditions and management of uric acid stones.

Results

The incidence of uric acid stones varies between countries and accounts for 5% to 40% of all urinary calculi. Hyperuricuria, low urinary output and acidic urine are well known contributing factors. However, the most important factor for uric acid stone formation is persistently acidic urine. Gout and myeloproliferative disorders are associated with uric acid stones. Why most patients with gout present with acidic urine yet only 20% have uric acid stone formation remains unclear. The pathophysiological basis for persistent urine acidity also remains unclear although various mechanisms have been proposed. Urinary alkalization with potassium citrate or sodium bicarbonate is a highly effective treatment, resulting in dissolution of existing stones and prevention of recurrence.

Conclusions

Acidic urine is a prerequisite for uric acid stone formation and growth. Medical management with urinary alkalization for stone dissolution and prevention of recurrence is effective and should be the cornerstone of treatment.

Primary hyperoxalurias are a devastating family of diseases leading to multisystem oxalate deposition, nephrolithiasis, nephrocalcinosis and end-stage renal disease. Traditional treatment paradigms are limited to conservative management, dialysis and combined transplantation of the kidney and liver, of which the liver is the primary source of oxalate production. However, transplantation is associated with many potential complications, including operative risks, graft rejection, post-transplant organ failure, as well as lifelong immunosuppressive medications and their adverse effects. New therapeutics being developed for primary hyperoxalurias take advantage of biochemical knowledge about oxalate synthesis and metabolism, and seek to specifically target these pathways with the goal of decreasing the accumulation and deposition of oxalate in the body.

Radioisotopic renal imaging proved to be much more sensitive than excretory urography in diagnosing renal parenchymal damage in 6 children with acute febrile urinary tract infections. This increased sensitivity may affect clinical management. More importantly, it may change the interpretation of scientific studies evaluating the natural history and treatment of vesicoureteral reflux.

Use of the word "benign" for all diseases that are not cancerous may suggest to patients that a life-threatening urologic condition is "innocuous" or even "harmless". We invite readers to propose alternative language that accurately describes the field of nononcologic adult urology, reflects the expertise of practitioners, and remains sensitive to the experience of patients.

Residual urine is important in the evaluation of the urological patient. The gold standard to obtain this information is a catheterized specimen. We examined the accuracy of a catheterized value to ascertain whether the bladder was emptied completely. After the bladder was catheterized 10 ml. radiocontrast material were instilled into the bladder to allow radiographic documentation of complete evacuation. We found that 26 per cent of 515 patients evaluated had residual urine after routine attempts were made to evacuate the bladder fully. We conclude that a single residual urine estimate may be inaccurate and one should not always base therapeutic decisions upon any single such measurement.

To determine whether extracorporeal shock wave lithotripsy can sterilize infection stones and, thus, decrease the recurrence rate we investigated its impact on the microbiological flora of staghorn calculi. Fragments from 17 staghorn calculi retrieved percutaneously were divided into paired sets. One set was fractured by extracorporeal shock wave lithotripsy at 18 kv. and with increasing numbers of shock waves up to 1,000. One set was fractured mechanically with a surgical clamp. Bacterial cultures were then compared between the 2 groups. Of the 17 staghorn calculi 10 showed significant bacterial growth (59%). The number of colony-forming units was not significantly different between stones fragmented by lithotripsy and those that were mechanically fractured. Furthermore, exposing fragments to an increasing number of shock waves did not alter the colony count. We conclude that extracorporeal shock wave lithotripsy has no discernible effect on the microbiological flora of infected staghorn calculi.