A friend emailed me last week. Her 6-year-old spayed female shepherd mix (“Gracie”) started leaking urine three weeks before; she urinates normally but also has an almost-constant slow drip at all other times, even when she’s asleep. When her owners first noticed the problem, they started taking her out to urinate as often as they could; but this didn’t help. They had taken her for a vet visit and were waiting for results from the lab work that was submitted. Gracie is about 10% over her ideal weight but appears otherwise healthy and active. The vet mentioned that the dripping is probably due to urethral sphincter mechanism incompetence (USMI). So, my friend wrote to me to find out more.
Gracie’s problem falls under the broad category of “urinary incontinence;” but dripping urine has a very different list of possible causes than, say, a dog that empties his entire bladder on the living room rug in the middle of the night or leaves a puddle by the front door when loud Uncle Ernie comes to visit. Leaking of urine can usually be attributed to one or more of only a few causes: anatomic abnormalities of the bladder and associated structures, diseases that cause increased water consumption, decreased urethral sphincter tone, and urinary tract infection. And, while the culprit can be a spinal cord injury, other neurological problem, or trauma, these are almost always accompanied by other signs.
What’s going on in Gracie’s case? It’s easy to rule out anatomic abnormalities as a single cause: she’s 6 years old and is only now showing signs of a problem. The results of the lab tests, which became available the day after my friend’s note, ruled out a urinary tract infection, endocrine diseases like Cushing’s or hypothyroidism, and kidney failure. So, that pretty much suggests USMI.
But, what specifically is USMI? The urethra is the tube that carries urine from the urinary bladder to the outside world. The urethral sphincter is the muscle that keeps the urethra from releasing urine until the individual chooses to. If this muscle fails, so does the individual’s control over urine being released. The exact causes of USMI are not completely understood; but they are believed to be a combination of low estrogen, advancing age, genetics, and obesity. Therefore, the prime candidate for this problem is an overweight large-breed female dog that has been spayed, thus reducing the amount of circulating estrogen. And, in fact, up to 20% of female dogs are affected By USMI.
To make a precise diagnosis, there is a way to measure the pressure exerted by the urethra; it’s called a Urethral Pressure Profile test and is available at specialty clinics. But, an initial diagnosis can be made based on the history provided by the owner and ruling out the other possible causes. Then, if treatments don’t work, the diagnostic tests can be used.
Treatments for this problem range from medications to the injection of collagen to firm up the sphincter. Medications include phenylpropanolamine (PPA), which enhances sphincter control, and estrogen, which increases the pressure applied by the sphincter. These medications can be used separately or together, but are not tolerated by all dogs. PPA can cause agitation, irritability, and blood pressure changes. Too much estrogen can cause vomiting and diarrhea, as well as anemia and reduced production of white blood cells. Other medications, although used less frequently, can relax the bladder to reduce dripping. An alternative to medication is the regular injection of collagen in to the urethra in an effort to reduce urine flow; this procedure is usually repeated every six months or so.
Gracie has started PPA and, although a bit edgy, appears to be handling it well. Her urine leaking has resolved completely. Her owners are keeping their fingers crossed.