Use of laser lithotripsy to treat urocystolishs in dogs: current status

In the 1970s, it was fortuitously recognized that shock waves generated by collision with raindrops produced unusual pitting patterns on the metal surface of supersonic aircraft during high-speed flight.

Researchers theorized that the elliptical contour of one part of the plane's fuselage resulted in the convergence of shockwaves onto another focal point of the aircraft, accelerating metal fatigue. Based on these observations, scientists at Domier, a German aerospace firm, embarked on a program to develop a system for the production of shock waves that could be reproducibly focused at a solitary point with the goal of fragmenting urinary stones.

This technique was called extracorporeal shockwave lithotripsy (ESWL). On Feb. 7, 1980, at the University of Munich, ESWL was used successfully to fragment uroliths in the kidney of a human patient (Chaussy 1989). Since that time, the development of ESWL has become a smashing success in terms of revolutionizing treatment of uroliths in man. Extracorporeal shock wave lithotripsy was followed by the development of intracorporeal techniques whereby instruments used to generate high-energy wavelengths were applied directly to the surface of uroliths viewed through an endoscope. Compared to surgery, lithotripsy is highly effective, minimally invasive and associated with less risk to the patient. Notably, use of ESWL shock wave lithotripsy and intracorporeal endoscopic laser lithotripsy to treat human patients with uroliths resulted in a significant reduction in iatrogenic loss of renal function associated with surgical intervention (Holman 2002).

Widespread knowledge of the success of extracorporeal and intracorporeal techniques of lithotripsy to treat kidney and ureteral stones in humans promoted veterinarians to consider its feasibility to manage uroliths in dogs. The result was development of effective protocols for ESWL to treat kidney and ureteral stones in dogs (Adams 1999). However, the majority of naturally occurring uroliths in dogs are located in the lower urinary tract rather than the kidneys and ureters. For example, uroliths from more than 200,000 dogs have been submitted to the Minnesota Urolith Center for analysis since 1981; in 98 percent of cases, uroliths were retrieved from the urinary bladder and/or urethra.

Unfortunately, ESWL is not a reliable form of treatment for bladder stones because of their tendency to move out of the focal point of converging shock-waves. Movement of the uroliths does not allow repeated shock waves to converge on a solitary point, resulting in reduced fragmentation. Fortunately, this obstacle has been over-come by fragmenting bladder stones with the aid of cystoscopes to guide various types of newly developed lithotriptors directly to the stone's surface. Although several forms of energy (electrohydraulic, ultrasonic, ballistic) can be delivered through the cystoscope, holmium:YAG laser technology effectively fragments all types of biogenic stones in dogs (Wynn 2002).

As illustrated in the following case report, cystoscopic laser lithotripsy is an effective alternative to surgical removal of urocystoliths.

•Case report A 5-year-old female spayed Miniature Schnauzer was referred by a colleague in Arizona to the University of Minnesota Veterinary Teaching Hospital because of a two-year history of recurrent bladder stones. Urocystoliths removed one year previously were composed of 95 percent magnesium ammonium phosphate and 5 percent calcium phosphate carbonate. Since that episode, this patient was fed canned and dry formulations of an adult maintenance food designed to reduce magnesium and to promote formation of acidic urine.

Physical examination revealed an alert dog weighing 12 kilograms. Temperature (102° F), respirations and pulse rate were normal. Serum concentrations of creatinine (1.1 mg/dl), urea nitrogen (SUN = 19 mg/dl), phosphorus (3.5 mg/dl), calcium (10.7 mg/dl) and bicarbonate (20 mmol/L) were normal. Results of a hemogram revealed values within the normal reference range (hematocrit = 56 percent and WBC = 7,880/ul). Analysis of a urine sample collected by cystocentesis prior to any form of therapy revealed that specific gravity was 1.032. The urine was alkaline (pH = 8.0) and contained numerous red blood cells (>50/hpf).

White cells and epithelial cells were not detected in urine sediment. However, a few amorphous calcium phosphate crystals were observed. Aerobic culture of an aliquot of urine collected by cystocentesis did not result in in-vitro growth of bacteria.