Urinary Incontinence

Causes of urine leakage in dogs:

Urinary incontinence (leaking of urine) occurs with alarming frequency in dogs, particularly in spayed females. Retrospective studies have reported that the incidence of urinary incontinence in dogs following ovariohysterectomy (spay) ranges from 13.6% to 20.1%. The significance of urinary incontinence in an indoor pet cannot be underestimated, as the problem can often lead to euthanasia due to repeated house soiling. Thus, urinary incontinence is a common problem with serious consequences.

Causes for urinary incontinence may be divided into two categories: anatomical abnormalities and functional abnormalities. The anatomical abnormality that is most often associated with urinary incontinence is ectopic ureter- a malformation in which the ureters empty into an inappropriate location, bypassing the sphincter that controls urine retention. Suspicion of ectopic ureter is highly dependent upon history and physical examination of the animal, as this problem occurs almost exclusively in female dogs and is characterized by constant dribbling of urine since birth. Functional abnormalities (failure of the urethral sphincter) causing urinary incontinence most commonly involve urethral sphincter mechanism incompetence (USMI), otherwise known as “hormone responsive incontinence”. In contrast to ureteral ectopia, USMI does not occur until later in life, after a dog is spayed and is characterized by intermittent urine leakage when dogs lay down or sleep. Other factors such as increased water consumption, urinary tract infections and vaginal malformations can exacerbate pre-existing incontinence, but in my opinion are rarely the primary cause.

Diagnosis:

One method of diagnosing a functional problem with the urethral sphincter is by response to treatment with drugs (typically with phenylpropanolamine, see later section). This method is not as simple as it seems, because a lack of response to treatment does not rule out sphincter dysfunction- up to 30% of dogs do not respond to drug therapy. In addition, many dogs require dosage adjustments and up to 4 weeks of drug therapy before a response is noted. Due to these issues, I believe that it is preferable to perform a proper diagnostic evaluation before pursuing therapy.

Diagnostic evaluation of urinary incontinence is focused primarily on identifying malformations or functional problems that can lead to urine leakage. Anatomic malformations (see previous section) may be identified through a number of imaging techniques. Initial screening examination is typically performed by use of x-rays or abdominal ultrasound. Abdominal ultrasound findings consistent with ureteral ectopia include a backup of urine on the affected side, causing enlargement of the affected ureter or kidney. In chronic cases, ascending bacterial infections may occur, causing serious kidney damage. Contrast studies are the classic method for identification of ectopic ureters. However, the technique is time consuming and can be difficult to interpret. We have switched to using urethroscopy- a technique in which a small camera is inserted into the urethra, allowing direct visualization of the ureteral openings. This technique is now considered the “gold standard” for diagnosis and can allow for simultaneous treatment of the condition at the same time through methods described below.

Treatment:

Drug therapy is the mainstay for treatment of urinary incontinence in dogs. The most commonly used agent is the alpha agonist phenylpropanolamine or PPA (drug name Proin). This drug has an efficacy of approximately 70% in resolving urine leakage due to sphincter malfunction in female dogs. Rare side effects of PPA include restlessness, poor appetite and high blood pressure. The effects of life-long administration of PPA have not been evaluated and the drug has not been consistently available. Despite these issues, PPA is currently the first line therapy for USMI in dogs due to its efficacy and minimal side effects.

Estrogenic compounds have also been demonstrated to have some efficacy in the treatment of USMI. Unfortunately, estrogens are associated with a risk of serious side effects, such as bone marrow suppression, skin changes and reproductive disorders. Due to these side effects, Estrogen is not typically used unless a dog has proven non-responsive to PPA therapy, or PPA is not available.

Surgical intervention is an option in dogs that fail to respond to pharmacological therapy. Techniques described in dogs with sphincter malfunction are similar to those used in human beings and have accomplished control of urine leakage by pulling the bladder forward into the abdomen, by urethral bulking, or through urethral sling procedures. The most commonly used surgical technique, colposuspension, was adapted from a technique used in women with increased mobility of the bladder and urethra after childbirth. The bladder is exposed through an incision in the abdomen. Sutures are placed into the vaginal wall pulling the bladder forward and into the abdomen. Though colposuspension has good short-term efficacy, surgery alone has produced poor long-term results, with restoration of continence in only 14-56% of dogs in large clinical studies. Many dogs that do not respond to surgery will benefit from continued administration of PPA.

A newer technique that is offered at VSES involves the use of minimally invasive surgery (MIS) to access the urethra and perform bulking injections with collagen. This technique has the advantage of decreasing both the cost and the discomfort involved with the abdominal surgery technique described above. Often, urethral collagen injection can be performed at the same time as diagnostic evaluation of the urinary tract, allowing immediate treatment of the condition. Efficacy is excellent in initial studies (>80%), although some dogs may need a second procedure later on in life if incontinence recurs over time.

Summary

Urinary incontinence is a common and serious problem in dogs. Primary rule outs include ectopic ureter and urethral sphincter mechanism incompetence. Diagnostic evaluation should include special imaging studies that can be obtained at VSES. Drug therapy is successful in the majority of dogs. For dogs that respond poorly to medical management, urethroscopy and collagen injections may offer a minimally invasive method for restoring continence.