USMI in dogs

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Is your dog leaking urine when she is sleeping or resting? If so, there is a good possibility that she has an incontinence problem that is commonly seen in spayed females. The symptom goes by several names:

• USMI - Urethral Sphincter Mechanism Incompetence
• Spay Incontinence
• Estrogen Responsive Incontinence
• Hormone Responsive Incontinence

Symptoms of Spay Incontinence

Although this condition can happen in male dogs, it is most commonly seen in spayed females. The most common symptom is finding puddles of urine in places where the dog sleeps or relaxes. If you are finding that your dog is occasionally "wetting the bed" then she may have USMI.

Dogs with this condition usually do not have an increase in thirst. They usually do not produce any more urine than usual. They are not usually acting or feeling sick at all.

What causes USMI?

Dogs can leak urine when the urethral sphincter loses some ability to function. The urethral sphincter is the part of the bladder that keeps the bladder closed. Imagine that you are using your fingers to pinch a balloon closed. If you loosened your grip, this would allow air to escape. The urethral sphincter is the set of muscles that keep urine from escaping from the bladder.

There are a few things that can contribute to this problem:

• As a dog ages, the muscles of the urethral sphincter can just naturally lose some strength.
• When a dog is spayed, there are changes in hormone levels. Some of these hormones help to keep the sphincter muscle strong. So, after a spay (often several years later) the muscles can start to lose some ability to stay tight.
• As a dog gains weight, more pressure is placed on the bladder by fat and organs in the abdomen.

How is USMI diagnosed?

There is no test for USMI. Instead, what we do is tests to look for other things that can cause incontinence and if we don't find a cause then we make an assumption that spay incontinence could be the culprit.

Sometimes a dog will become incontinent because there is a condition that is causing her to produce more urine than normal. Some examples are kidney disease, cushing's disease or diabetes. Some infections can also cause incontinence too.

If your vet does urine tests and everything is normal, then they likely will suggest treatment with a medication to help keep the urethral sphincter closed.

Treatment of USMI

There are two ways that vets will treat this type of incontinence:

Phenylpropanolamine (PPA, Proin): This medication works directly on the muscle of the urinary sphincter to help it stay closed. Most dogs will need to take the medicine two to three times daily. While it is generally safe, there are some dogs who will have side effects including a fast heart rate, high blood pressure and restlessness or agitation.

Diethylstilbestrol (DES, Estrogen): This medication is an estrogen supplement. I prefer to prescribe this medication because for most dogs it only needs to be given once or twice per week as opposed to several times daily for PPA. Estrogens work for this problem by improving the function of the nerves of the urinary sphincter. This gives the sphincter a greater ability to stay closed.

There are some vets who do not like to prescribe DES to dogs because there is a concern that it will cause a serious red blood cell problem called aplastic anemia. However, this condition is only seen when extremely high levels of DES are prescribed.

In some areas, DES is not available. Veterinarians often will have a compounding pharmacy make this medication for them. However, a new drug, called Incurin (see below) may be an alternative.

Estriol (Incurin): On July 27, 2011, the FDA announced that a new drug has been approved to treat urinary incontinence in dogs, called Incurin. Incurin is very similar to Diethylstilbestrol (DES). It works by increasing the muscle tone of the urethra. As this drug has a label for use in dogs, it will likely become the most prescribed medication for USMI.

Some dogs will need a combination of PPA and DES (or Incurin) in order to stay continent.

Your dog will likely need to stay on medication for the rest of her life in order to keep from leaking urine.

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