Urinary incontinence (lack of the control of urination) is distinguished from other causes of inappropriate urination by the fact that it occurs without the dog being aware, such as when she is sleeping. Dribbling urine and leaking at night are signs of incontinence. There are several physiological reasons that urinary incontinence occurs, but the most common problem is associated with reproductive hormone (estrogen) levels in older spayed female dogs. This topic does not address pathological, infectious, or behavioral reasons for inappropriate elimination or house training issues.
The dog’s history of symptoms and a urinalysis can quickly rule out a bladder infection or kidney disease as being the cause of bed wetting. Excessive water consumption due to underlying diseases like Diabetes and Cushing’s should be ruled out as well. In the case of hormone related urinary incontinence, the urine is completely normal. It should be noted however, that incontinent dogs are more susceptible to ascending bacterial bladder infections because of the mechanism that causes the bladder to leak.
The cause of estrogen responsive urinary incontinence is not completely understood, but the fact that it occurs in spayed females and responds to estrogen supplementation leads us to believe that the mechanism involves reduce levels of the hormone or reduced estrogen-receptor function. Urine is kept in the bladder by a sphincter muscle at the top of the urethra, the tube that carries urine outside the body. In older spayed female dogs, this sphincter muscle loses tone, and urine begins to leak. During rest and sleep, the muscles especially relax, leading to complete incontinence. Obesity further complicates this condition, probably from excess weight pushing on the bladder. Not all spayed female dogs will develop urinary incontinence; therefore, the exact role that estrogen plays is uncertain.
Supplementation with synthetic estrogen will correct incontinence in about half of symptomatic dogs. Diethylstilbestrol (DES) is the drug that is most commonly prescribed. Overdosage carries serious side effects, and long term usage can occasionally cause bone marrow suppression leading to reduced blood cell counts. People should not handle the medication. Overall, DES has a good margin of safety, but unavailability and less than ideal response to the drug has caused doctors to seek alternative therapies.
Phenylpropanolamine (PPA) is a stimulant drug that helps strengthen bladder muscle tone. It is effective in controlling estrogen-responsive urinary incontinence in 85-90% of dogs. PPA has a wide margin of safety; however, it should be used with caution in dogs with heart or kidney failure, or those with high blood pressure, because of its stimulant effect. Side effects may be controlled by lowering the dose, but efficacy in controlling incontinence may be reduced.
A combination of the two drugs may be used in dogs that do not respond to single drug therapy, or for those dogs who do not tolerate high doses of either. If incontinence suddenly becomes more frequent, or accidents occur when the pet is not at rest, a bacterial infection should be considered as a complicating factor.