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Nonsurgical urolith management (Proceedings)

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Aug 01, 2010

Successful management of urolithiasis in dogs and cats depends upon the removal of existing uroliths and preventing their recurrence. Traditionally, uroliths have been removed via surgery. However, depending on the location, size, number and composition of the uroliths, less invasive techniques may be equally as effective. Options for non-surgical stone removal include; medical dissolution, spontaneous voiding, catheter retrieval, voiding urohydropulsion, basket retrieval, laser lithotripsy, and extracorporeal shock wave lithotripsy. Although many types of uroliths tend to recur, careful management and frequent monitoring may help to minimize recurrence. Although there are many acquired disease conditions that can contribute to stone formation, many animals (and people) are genetically predisposed to developing specific stones types (e.g. Dalmatians and urate stones). To avoid incorrect assumptions (and thus therapy) concerning the mineral composition of uroliths, all uroliths that are retrieved should be submitted for quantitative mineral analysis. The Minnesota Urolith Center will analyze uroliths at no charge; submission forms are available online.

The first step to preventing new stone formation is to ensure that all current stones are removed. The most common cause of rapid recurrence of uroliths is incomplete removal. If any small stones are left in the bladder they act as scaffolding resulting in the formation of larger stones quickly. Stones are frequently left behind following cystotomy as flushing fluid through the urethra may not be a reliable method of moving uroliths. This is especially true for uroliths with an irregular contour (e.g. calcium oxalate and silica) which allow catheters and saline to slide pass uroliths lodged in the urethral lumen. To verify complete urolith removal, radiograph the entire urinary tract immediately after any stone removal procedure. If uroliths are detected, consider their immediate removal as long as the patient is stable. Without post-surgical radiography, it will be difficult to distinguish recurrence of the uroliths from failure of removal as a cause for recurrence of clinical signs.

Options for non-surgical stone removal

1. Medical dissolution

Medical dissolution is the least invasive method of stone removal, but is only effective for certain types of uroliths in certain locations. Uroliths that may be medically dissolved include only struvite, urates, and cystine. Calcium oxalate and silica uroliths cannot be medically dissolved. For dissolution to occur, the uroliths must be surrounded by/bathed in dilute urine of the proper composition to allow the crystals to go back into solution. This is most likely to occur in the bladder. Nephroliths, urethraliths and ureteroliths are less likely to dissolve. A calculolytic diet specific to the stone type in question must be fed exclusively throughout the dissolution. In dogs, the majority of struvite stones result from urinary tract infections that change the urinary pH, thus strict infection control is essential for dissolution. Antimicrobial therapy must be given throughout the entire dissolution period as viable bacteria are contained within layers of struvite uroliths. Antibiotic and dietary therapy should be continued for at least 1 month following radiographic dissolution of the stones. Once uroliths are removed, preventative therapy should be initiated to reduce recurrence.

2) Spontaneous Voiding

Very lucky patients may spontaneously void their stones. Due to the anatomy of most quadripeds, the dependent portion of the bladder is located below the outflow tract, predisposing to the retention of bladder stones. Unfortunately, even the most well-behaved and obedient patients are not likely to urinate on command while standing on their hind legs. However, occasionally, a patient will void small stones during forceful urination, or if the stones become suspended in solution after exercise. Owners may be instructed to collect urine at home and strain through a fine meshed fish net in order to collect stones for analysis.