Prospective Evaluation of Urodynamic Testing in Dogs Undergoing Stent Placement to Relieve Malignant Urethral Obstruction
Cancer resulting in obstruction of the lower urinary tract of dogs is most commonly found in the prostate, urinary bladder and urethra (tube responsible for draining urine out of the body). When cancer occurs in this region, abnormal signs include increased frequency of urination, difficulty urinating (straining) and blood in the urine. Unfortunately, cancer of the lower urinary tract often results in complete blockage of the urethra causing a patient to be unable to pass urine. The inability to urinate is a life-threatening emergency as severe electrolyte abnormalities and abnormal heart rhythms can occur.
The mainstays of treatment for prostate, bladder and urethra cancer are surgery, chemotherapy, radiation therapy, or a combination of these treatments. However, these treatments are essentially ineffective in relieving an acute obstruction of the urethra, as their effects are not immediate. A palliative technique involving the placement of a metal or alloy stent within the urethra has been performed in dogs, cats and humans. The stent forces the urethra open by pushing the tumor outward, thus allowing the patient to urinate. Urethral stent placement has been shown to be effective in relieving urethral obstructions in dogs. Urethral stents are an important treatment option as these provide almost immediate improvement in a condition that might otherwise be fatal.
The major complication associated with urethral stent placement in dogs is urinary incontinence which has been reported to occur in at least 25% of cases. When urinary incontinence occurs, the dog is unable to control the passage of urine which can result in skin irritation and sores, and an increased risk for development of urinary tract infections.
The pressure within the bladder and urethra can be measured by placing a pressure monitor directly into these organs. This device has been used with success in humans and companion animals in the evaluation and treatment of urinary incontinence. The urethral and bladder pressures of dogs with cancer-induced urethral obstructions and dogs with urethral stents have not been reported. The goal of this project is to determine the urethral and bladder pressures of dogs with cancer-induced urethral obstructions and in dogs with urethral stents. In doing so, we hope to use these results to potentially decrease the development of urinary incontinence secondary to urethral stent placement. Also, with the data obtained in this study, we hope to improve our ability to inform owners of the chance that their dog will or will not likely develop urinary incontinence and develop therapeutic agents aimed at decreasing incontinence.