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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 (Macroplastigue, Urolplasty, Inc., Minnetonka, MN), 77% of dogs were continent. CellFoam VetTM 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
An Urban Experience
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 increased
to 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
Arnold S, Arnold P, Hubler M, et al. Urinary incontinence in spayed female dogs: frequency and breed distribution. Schwez Arch Tierheilkd 1989;131:259-263.
Barth A, Reichler IM, Hubler M, et al. Evaluation of long-term effects of endoscopic injection of collagen into the urethral submucosa for treatment of urethral sphincter incompetence in female dogs: 40 cases (1993-2000). JAVMA 2005; 226:73-76.
Berent A. Endoscopic treatment of ectopic ureters: Short & long term outcomes using cystoscopic-guided laser ablation (CLA-EU). Proceedings of the 2011 ACVIM Forum, 2011.
Berent A, Weisse C, Adan C and Todd K. The use of a percutaneously controlled hydraulic occluder for the treatment of urethral sphincter mechanism incompetence in 11 dogs and 1 cat. JVIM 2009; 23:689 (abstract).
Rose SA, Adin CA, Ellison GW, Sereda CW, Archer LL. Long term efficacy of a percutaneously adjustable hydraulic urethral sphincter for treatment of urinary incontinence in four dogs. Vet Surg. 2009; 38:747-53.
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