It is estimated that 20% of dogs in the United States will develop urinary incontinence. Urethral sphincter mechanism incompetence (USMI), ectopic ureters, paradoxical incontinence, detrusor hyperactivity, vestibulovaginal abnormalities, and neurologic disorders are all causes of urinary incontinence in dogs. Signalment, historical information, and the pattern of incontinence can lead to an accurate diagnosis most of the time. In more complicated cases advanced imaging studies or cystourethroscopy or both may be needed to render a diagnosis. Standard medical therapy can be used to effectively treat 85–90% of dogs with USMI and some dogs with ectopic ureters. Dogs with refractory incontinence can be very challenging to pet owners and veterinarians and require other forms of management. The purpose of this presentation is to discuss advances in medical management of dogs with refractory incontinence.

Medical Management

Appropriate medical management depends upon the underlying cause of urinary incontinence. Alpha agonists and reproductive hormones are the most common agents used for the treatment of USMI, the most common form of urinary incontinence in mature female dogs. Reported success rates of the alpha agonist phenylpropanolamine (PPA) in female dogs with USMI have been as high as 90%. Some dogs may take as long as 4 weeks to demonstrate a complete response. Ephedrine and pseudoephedrine are alternative alpha agonists that can be used for the treatment of USMI, but have slightly lower success rates than PPA. These drugs should be avoided in dogs with cardiac disease or hypertension. Diethylstilbestrol (DES) has historically been the most common reproductive hormone used in the management of USMI in female dogs and is reported to have a 60–80% success rate. Estriol is now commercially available and has similar response rates. Some female dogs that fail to become continent with PPA or DES will exhibit continence when the drugs are given as combination therapy. Gonadotropin releasing hormone analogues, such as leuprolide, buserelin, triptorelin, or deslorelin, have also been be used to control incontinence with efficacy rates of 50–70%. They work by down-regulating LH secretion to restore continence and may be more effective when combined with PPA.

Male dogs with USMI have a lower and less predictable response rate to alpha agonists (<50%) but may respond to injections of testosterone cypionate given every 6–8 weeks. The low response rate in males might be due to the difficulty in differentiating detrusor weakness from urethral incompetence.

Urethral Bulking Agents

Refractory USMI may be managed by submucosal injection of bulking agents in the proximal urethra during cystourethroscopy. Submucosal bulking creates a central filling volume that in turn increases the length of the muscle fibers and closure power of the urethral sphincter thereby increasing resistance to urine flow. Generally, the bulking agent is injected in 3–4 sites around the circumference of the proximal urethra (just distal to the trigone) until the deposits close the urethral lumen, as seen through the cystoscope. Mild complications (e.g., dysuria) occur in up to 15% of dogs in the immediate post-procedural period. Success is usually apparent within 1–3 days.

Purified bovine collagen that has been cross-linked with glutaraldehyde is the bulking agent that has been used most commonly in veterinary medicine. Submucosal collagen injections are effective at restoring continence in approximately 65% of dogs, with an additional 15% achieving continence after adding standard medical therapy. Approximately 10% of dogs will demonstrate improvement with collagen injections and standard medical management but will not be completely continent and the remaining 10% will not have any demonstrable improvement after injection. Continence is not permanent and most dogs requiring subsequent injections within 12–18 months. Mild complications (e.g., dysuria) occur in up to 15% of dogs in the immediate post-procedural period.

Other agents have been used for bulking. At one month after injection of polydimethylsiloxane (Macroplastique, Uroplasty, Inc., Minnetonka, MN), 77% of dogs were continent. CellFoam Vet™ is currently being studied for use in dogs with USMI; preliminary results suggest a high rate of continence following injection.

Artificial Urethral Sphincter

There has been increased interest in a novel surgical option for dogs that have failed medical management. The artificial urethral sphincter (hydraulic urethral occlude) is an inflatable silicone ring that is surgically placed around the proximal urethra and connected to a subcutaneous injection port. Some dogs achieve continence following placement of the device. Other dogs return for inflation of the device approximately one month after surgery. The device appears to be approximately 90% effective and may be a successful option for the long-term control of incontinence in dogs. Owners should be forewarned that the procedure could have serious complications (e.g., extraluminal stricture, obstruction to urine outflow, intraluminal webbing, hydroureter, and hydronephrosis).

Regenerative Medicine Approach

The normal urethra consists of layers of striated muscle, smooth muscle, connective tissue, submucosal vascular plexus, and epithelium. The striated muscle layer appears to contribute the most to maintenance of urethral tone and continence. Certain stem cells differentiate into striated and smooth muscle cells. When injected into the urethra, these stem cells have the potential to restore the musculature. Injection of muscle-derived stem cells, obtained from skeletal muscle biopsies, have been used for the regenerative repair of deficient sphincter muscle in women with urethral incontinence who failed traditional medical therapy. Improved continence rates of up to 89% were reported 2 years following injection in women. A regenerative medical approach for urethral incontinence was studied in dogs that had induced urinary sphincter insufficiency following urethral damage. Six months after autologous muscle progenitor cells isolated from skeletal muscle biopsies were injected into the damaged sphincter, dogs had urethral pressures that approximated 80% of normal compared with control dogs that remained at around 20% of normal. Ongoing clinical trials suggest that urethral injection of autologous muscle progenitor cells can also lead to improvement or resolution of urinary incontinence in female dogs presumed to be secondary to naturally acquired urethral sphincter mechanism incompetence.

Endoscopic Treatment of Ectopic Ureters

Ectopic ureters represent an abnormal development of the urinary system where one or both ureteral orifices can be found distal to the trigone of the bladder and are the common cause of urinary incontinence in juvenile female dogs. Most ectopic ureters are intramural, entering the bladder at a normal location but tunneling in the submucosa to a distal opening. The remaining (<5%) are extramural, implanting at a distal location. Between 70–94% of dogs with ectopic ureters have other abnormalities of the urinary tract including hydroureter, hydronephrosis, ureterocele, pelvic bladder, renal dysplasia, renal agenesis, persistent paramesonephric remnant, hypoplastic urinary bladder, short urethra, chronic UTI, and USMI. All dogs suspected of having ectopic ureter should undergo a thorough clinical evaluation before any corrective procedure. Cystoscopy is 100% accurate in the diagnosis. Dogs with intramural ectopic ureters can undergo cystoscopic laser ablation; surgical correction is required for extramural ectopic ureters. Approximately 50–60% of dogs will have resolution of incontinence following the procedure. The rate of incontinence can be decreased as much as 80% with additional management (i.e., medical, urethral bulking). Approximately 15–20% of dogs with ectopic ureters will remain incontinent regardless of the method used to treat them. There is no evidence to date to suggest that laser ablation is better than surgery in achieving continence in affected dogs. The advantage of cystoscopic laser ablation is that the hospitalization time is shorter and there is less pain associated with the procedure. Because it is minimally invasive, it would also be reasonable to assume that laser ablation would be associated with fewer complications than would surgery but this has not been demonstrated clearly.

References

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3.  Berent A. Endoscopic treatment of ectopic ureters: Short & long term outcomes using cystoscopic-guided laser ablation (CLA-EU). In: Proceedings of the 2011 ACVIM Forum; 2011.

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