Urethral Sphincter Mechanism Incompetence (USMI) is the most common cause of urine incontinence in adult dogs.
It is typically seen in older, larger breed, neutered females.
Dogs are not aware that they are leaking urine – it's not deliberate weeing!
It can normally be treated very successfully with medication.
What is the ‘urethral sphincter’ and what happens when it doesn’t work?
The ‘urethra’ is the pipe which carries urine from the bladder to the outside of the body. It contains muscles within the wall which contract to close the pipe and stop the urine escaping. This is very similar to a valve in household plumbing. With USMI, these muscles become weak and floppy (‘incompetent’) and cannot close the pipe fully, so urine leaks out when it shouldn’t. Dogs are unaware that this is happening.
What are the signs of USMI?
Dribbling urine – especially at rest, when lying down or sleeping
Staining of the fur around the penis or vulva from leaking urine
Repeated urinary tract infections (cystitis).
What are the risk factors?
The precise cause of USMI is still not fully understood but there are many factors which have been identified as increasing the risk of a dog developing it.
Female dogs
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Breed – this can occur in any breed, but a much higher number of cases are seen in medium to large breed dogs, with the following breeds thought to be most commonly affected:
-Doberman
-Springer Spaniel
-Old English Sheepdog
-Giant Schnauzer
-Boxer
-Irish Setter
-Rottweiler
-Weimaraner
Older dogs
Overweight dogs
Tail docking
Position of the bladder - having a bladder that sits further back in the abdomen and closer to the pelvis increases the risk.
Neutering – The incidence of USMI in spayed dogs is thought to be between 5-20%, with signs usually developing about 3 years after neutering. However, the link between spaying and developing USMI is not fully understood. It is thought that the link has something to do with the reduction in the female sex hormone oestrogen, however this is not thought to be the only factor.
Early neutering – there is weak evidence to suggest that there is an increased risk of developing USMI if your female dog is spayed before three months of age.
Dogs with a short urethra
What treatment is my vet likely to advise?
Most cases are managed effectively with daily medication which improves the tone in the muscle wall of the urethra, so the urine pipe closes tighter and does not leak.
The most common medications used contain the active ingredient Phenylpropanolamine. This comes as a liquid which can be added to your dog’s food daily. This treatment has been found to be effective in about 85-90% of patients.
Other medications include Estriol (an oestrogen). These tablets are often used in combination with phenylpropanolamine (in particular those cases which are less responsive to treatment). Their combination can prove to be more effective than using either medication alone.
What if medication doesn't work?
In the few cases that do not respond to medical treatment, surgical treatment is then considered. This includes various techniques designed to either tighten the urethra (collagen implants or placement of an artificial urethral sphincter) or relocate the bladder further forwards into the abdominal cavity (Colposuspension surgery).
What happens in the long-term?
Once treatment has been initiated, your dog will probably remain on this medication for life.
With time, the medication can become less effective and so the dose may need to be increased or other medications added. It is important therefore, to keep an eye on any changes in your dog’s urinating habits and discuss these with your vet.
Dogs with USMI are also more prone to developing urinary tract infections (cystitis).
Signs to look out for include:
Frequent weeing
Straining to pee
Passing only small amounts of urine
Passing urine containing blood.
Contact your vet immediately if you notice any of these signs as early intervention is important.
