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Pyometra: What is it and Why Does it Happen?

dr-emily-finnby Emily Finn, DVM

MSPCA-Angell West, Waltham

One of the most common reproductive emergencies seen in a veterinary emergency room is a condition called pyometra.  The name of this disease is Latin for “pus-uterus” and describes a life threatening uterine infection that most typically affects older, intact (or unspayed), female dogs. As intact female dogs age, the hormones that fluctuate during each heat cycle change the uterus – it becomes thicker and engorged with tissue to support potential pregnancy.  As these changes occur year after year, the uterus can be permanently changed – it becomes thicker and engorged with excess tissue. These changes make the uterus especially prone to developing infection and quite poor at fighting off infection if it does occur.

The uterus is most susceptible to infection about 1-2 months after each heat cycle. While the uterus is normally a sterile, internal organ the healthy vagina is full of bacteria. When colonizing external organs, these bacteria do not cause problems – in fact, they help maintain the body’s health. If these bacteria cross the cervix, though, and enter the uterus, infection may take hold. If this happens, pyometra develops.

If an intact female dog comes into the emergency room for changes in energy level, changes in appetite, “seeming sick,” or increased thirst and urination, pyometra is one of the diseases for which we will want to check.  Some dogs with pyometra will have pus coming from the vagina. Unfortunately, other times the cervix is tightly shut and does not allow the pus to leak out from the uterus – because the issue is less obvious to their families, these dogs, which are typically sicker, come into the ER later in the course of their disease. While surgical removal of the infected uterus is the treatment of choice for this condition, dogs with a “closed pyometra” (the pus is unable to leak out) need surgery sooner and tend to need more aggressive management.  Occasionally, if the sick dog comes into the hospital quite late in the course of her disease, the uterus will have become so compromised that it ruptures and the pus fills the abdomen.  These dogs have what is called a septic abdomen and are very sick. Prognosis is considerably poorer for dogs with a ruptured pyometra.

Emergency pyometra surgery is best avoided with routine spaying

Emergency pyometra surgery is best avoided with routine spaying

Diagnosis and treatment

If your dog comes into the hospital with the above described signs, often our first steps will be to do a physical exam, draw some basic lab work, and get x-rays. Lab work may show dehydration, high white blood cells (indicating an activated immune system) and, if your dog is very sick, we may see significant changes in electrolytes, blood sugar, kidney, and liver values. X-rays can show a distended, fluid and/or gas filled uterus. If the uterus is draining pus, though, it may appear normal.  If the diagnosis is not confirmed by physical examination, lab work, and x-rays, an ultrasound can be done to more directly visualize the uterus and determine its degree of abnormality.

As the diagnostics are being collected (or shortly after confirmation of diagnosis), your dog will have an IV catheter placed.   Depending on how sick she is and if she is acting uncomfortable, she will receive intravenous fluids and pain medications. Often times, antibiotics will be started. As soon as your dog is stable enough for anesthesia (as determined by blood pressure, heart rate, and mentation), she will be taken to surgery for removal of the infected uterus as well as the ovaries. It is essential that both the uterus and the ovaries are removed, as the ovaries would continue to make the hormones that allowed the pyometra to develop in the first place if left.  Dogs who have had pyometra surgery often feel much better soon after they fully wake up from anesthesia. The infected organ has been removed and hence both the infection as well as the source of discomfort has been removed.  Dogs who have signs of sepsis (either from a ruptured uterus or long standing pyometra that has allowed bacteria to leak into the bloodstream) will take longer to feel better, though surgery may still be curative.

Rarely, non-surgical options will be discussed as management of pyometra.  This option is reserved for dogs with open pyometra (the dogs in which the pus is leaking out) who have a very high breeding value.  Certain hormones can be given by injections that help the uterus to contract and expel the infection. These contractions, though, are quite uncomfortable for the dog and increase the risk of uterine rupture. This treatment requires a week of hospitalization and is often considerably more expensive than surgery.  It is essential that the dog is bred during the next heat cycle, though many dogs are unable to carry pregnancy due to scarring of the uterus. Finally, the rate of having another pyometra is quite high (potentially greater than 75%), so the decision to pursue medical therapy must be arrived at very carefully. Again, only dogs which contribute significant value to the breeding population and with the ideal clinical presentation should be considered for this option.


The best and only prevention for pyometra is to have your dog spayed. Spaying (whether by removing the uterus and ovaries or just the ovaries) removes the hormonal stimulation that causes both heat cycles and the uterine changes that allow pyometra to happen. It is considerably safer (and less expensive) to spay a healthy dog with a healthy uterus than it is to take a sick dog with an abnormal uterus to surgery.  The current recommendation is to have female dogs spayed prior to their first heat cycles, but most older dogs are also good candidates for undergoing the spay procedure. Speak with your family veterinarian about the spay procedure, its risks, and its benefits.

For more information about Angell’s Emergency/Critical Care service, please visit or call MSPCA-Angell West inWaltham at 781-902-8400.

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