Tech Talks: Pyometra

Tech Talks by Emily Harbury, LVT

The Latin root for the word pyometra is “pus” (pyo) and uterus (metra). Pyometra is an abscessed, pus-filled. infected uterus. Toxins and bacteria leak across the uterine walls and into the bloodstream, causing life-threatening toxic effects. The uterus dies, releasing large amounts of pus and dead tissue into the abdomen. Without treatment death is inevitable. Prevention of this disease is one of the main reasons for routinely spaying female dogs.

 Classically, the patient is an older female dog. Usually, she has finished a heat cycle in the previous 1 to 2 months. She has a poor appetite and may be vomiting or drinking an excessive amount of water. There are two types of pyometra “open pyometra” is the more common and has the better prognosis. The cervix is open and the purulent uterine contents can drip out so that a smelly vaginal discharge is usually apparent. This is what alerts owners early in the disorder to seek veterinary help. The other type is a “closed pyometra” where the cervix is closed. In these cases, there is no vaginal discharge and the clinical presentation is more difficult to diagnose. These patients also tend to be sicker than those with open pyometra due to retention of the toxic uterine contents as well as a longer disease course prior to diagnosis.

Lab work shows a pattern typical of widespread infection that is often helpful in narrowing down the diagnosis. Radiographs may show a gigantic distended uterus, though sometimes this is not obvious and ultrasound is needed to confirm the diagnosis.

How does this Infection Come About?  

With each heat cycle, the uterine lining engorges in preparation for pregnancy. Sometimes, tissue engorgement becomes excessive or persistent (a condition called cystic endometrial hyperplasia). This lush glandular tissue is ripe for infection (while the inside of the uterus is sterile, 5 the vagina below is loaded with bacteria). Bacteria ascend from the vagina into the uterus, which becomes infected and ultimately filled with pus. Hormonal effects on the uterine tissue accumulate with each heat cycle, which means pyometra is much more common in older females because they have experienced many hormonal cycles.

Traditional Treatment: Surgery

The treatment for pyometra is surgical removal of the uterus and ovaries. It is crucial that the infected uterine contents do not spill and that no excess bleeding occurs. The surgery is challenging, especially if the patient is septic. Antibiotics are given at the time of surgery and will be continued after the uterus is removed. Pain relievers are often needed post-operatively. A few days of hospitalization are typically needed after the surgery is performed.

It is especially important that the ovaries be removed to prevent future hormonal influence on any small stumps of uterus that might be left behind. If any portion of an ovary is left, the patient will continue to experience heat cycles and be vulnerable to recurrence. While pyometra surgery amounts to the same result as routine spaying, there is nothing routine about a pyometra spay. As noted, the surgery is challenging and the patient is in a life-threatening situation. For these reasons, the pyometra spay typically costs five to ten times as much as a routine spay.  

With surgery, the infected uterus is resolved rapidly (in an hour or two of surgery) and there is an extremely limited possibility of disease recurrence. However surgery must be performed on a patient who could be unstable and the dog is sterile afterwards.  

Alternative Treatment: Prostaglandin Injections

In the late 1980s another treatment protocol became available that might be able to spare a valuable animal’s reproductive capacity. Here, hormones, called prostaglandins, are given as injections to cause the uterus to contract and expel its pus. A week or so of hospitalization is necessary and some cramping discomfort is often experienced. This form of treatment is not an option in the event of closed pyometra because the closed cervix prevents drainage of the infected material even in the face of prostaglandin contractions. Further, the dog must be bred and conceive on the next heat cycle. If she is not bred or does not conceive puppies on the next heat cycle, the recurrence rate of pyometra may be as high as 77%. After recovery from pyometra, the uterus is damaged and may not carry a litter normally (50-65% pregnancy rates with breeding have been published). Unless the dog has great value to a breeding program, it may not be worth it to attempt prostaglandin treatment. Personally, I have never seen this alternative attempted.


Spaying represents complete prevention of this condition. The benefit/risk of spaying your adult dog is a hot button topic that I don’t want to go into in this discussion. We know that pyometra is impossible in a spayed animal. An intact female, past her reproductive age, can be spayed and completely removes the possibility of pyometra as well as uterine or mammary cancer.

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