Minimizing pseudo-recurrent urolithiasis



DIAGNOTES
Case scenario: A 4-year-old male neutered Dalmatian with a history of ammonium urate urolithiasis was admitted to a veterinary hospital because of clinical signs presumed to be related to obstruction of the urethra caused with uroliths.


Figure 1: Double contrast cystogram of the dog described in Figure 1. There are three uroliths in the bladder lumen.
The owner had observed the dog unsuccessfully straining to void urine for the past 24 hours. Survey and contrast radiography confirmed the presence of numerous uroliths in the lumen of the urethra and urinary bladder (Figure 1). Using retrograde urohydropropulsion, the urethroliths were returned to the urinary bladder by the emergency staff. As the dog was not azotemic and was otherwise healthy, a cystotomy was performed, and more than 100 uroliths were removed. Analysis of the uroliths revealed that they were composed of 100-percent ammonium urate.

At the time the dog was released from the hospital, the owners were advised that a management protocol designed to minimize risk factors associated with ammonium urate uroliths should be seriously considered. This encompassed using a high-moisture (canned) diet designed to restrict purines and to promote formation of dilute alkaline urine (Prescription Diet Canine u/d, Hill's Pet Nutrition).


Jody P. Lulich
Twelve days later, the dog was returned to the hospital for removal of abdominal skin sutures. According to the owner, the dog was pollakiuric for the first week following surgery. For the past two to three days, he was dysuric and voided an abnormally small stream of urine.


Figure 2: Retrograde positive contrast urethrocystogram of a 4-year-old male Dalmatian illustrating numerous ammonium urate uroliths in the bladder and urethra.
Palpation of the dog's urethra per rectum revealed at least two uroliths causing partial urethral outflow obstruction. Follow-up contrast radiography confirmed that three uroliths were present in the urethra. Because the uroliths were smooth, they were readily repulsed into the urinary bladder by retrograde urohydropropulsion. Double contrast cystography revealed that three uroliths were in the bladder lumen at that time (Figure 2). The three uroliths were approximately 0.5 cm in diameter.


Carl A. Osborne
This prompted the owners to ask whether or not the stones had reformed during the 12-day post-surgical interval. Unfortunately, postoperative radiographs were not evaluated immediately following the cystotomy to determine if all of the stones had been removed. Study of the biological behavior of urate urolithiasis in Dalmatians indicates that recurrence of uroliths in this patient within the 12-day period following surgery is highly improbable. In our opinion, failure to remove all the uroliths by cystotomy was a medical mistake (e.g. an iatrogenic complication).

Understanding the cause

How common is pseudorecurrent urolithiasis? Several years ago, we performed a retrospective study of cystotomies performed to remove uroliths from 37 dogs and 29 cats in our veterinary teaching hospital (Lulich J, Osborne C, et al. Incomplete Removal of Canine and Feline Urocystoliths by Cystotomy. J Vet Int Med; 7: 124, 1993). Incomplete removal of uroliths was documented and revealed incomplete removal in eight dogs and four cats. The observation that uroliths were detected in the lower urinary tract following cystotomy in 20 percent of cats and 14 percent of dogs in a teaching hospital with board-certified surgeons on the staff emphasizes an inherent risk associated with this procedure. In our experience, based on consultations with our colleagues in private practice, incomplete removal of uroliths occurs much more frequently than is recognized.


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Why? Because radiography of the urinary tract immediately following surgery has not been a standard practice. A common theme is discovery of remaining uroliths several weeks or months following surgery when patients are re-evaluated because of persistent or recurrent signs of lower urinary tract disease. In this situation, delayed detection of uroliths is often erroneously attributed to recurrence (pseudo-recurrence). This, in turn, may result in inappropriate prognostic and therapeutic recommendations.

Consider the options

How can pseudorecurrent urolithiasis be minimized?

One should consider the following procedures.