Pyometra and Cystic Endometrial Hyperplasia in Dogs

Stephanie Howe, DVM
By Stephanie Howe, DVM on Feb. 3, 2022
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In This Article


What Is Pyometra in Dogs?

A pyometra is a severe bacterial infection in the reproductive tract that causes the formation of purulent (pus or containing pus) material to develop in the uterus. This occurs secondary to hormonal changes in female dogs. 

Cystic endometrial hyperplasia is often used synonymously with the term pyometra, and while these terms are often associated with one another they are not the same. Cystic endometrial hyperplasia is a thickening of the uterine tissue which then makes for an ideal environment for a pyometra to occur. 

Bacteria and toxins from the infection can leak through the wall of the uterus and into a dog's bloodstream, causing a body-wide infection (sepsis). The uterus becomes very fragile, and pus can start to leak into the abdomen. 

Without treatment, this can be a life-threatening condition. 

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Symptoms of Pyometra in Dogs

The symptoms of a pyometra can be vague, and it may resemble other types of infectious diseases. Generally, a veterinarian would become suspicious of a pyometra in a dog that finished her heat cycle about 1-2 months earlier and has one or more of the following symptoms:  

  • Pustular to bloody vaginal discharge 

  • Poor appetite 

  • Vomiting/diarrhea 

  • Drinking a large amount of water 

  • Lethargy/depression 

  • Fever 

With an “open” pyometra, the cervix is open, and the infectious material inside the uterus leaks out through the vagina/vulva. You may see a small to moderate amount of this pustular material on your pet’s vulva or tail, but you may also notice it on your pet’s bed or where she has been sleeping. 

However, a pyometra can also occur with a closed cervix. In this case, no discharge will be able to escape the uterus, making diagnosis more difficult. Since the infection is trapped inside the body, these dogs present with more serious symptoms. 

While this is a disease of non-spayed females, there can be a very rare infection of the uterine tissue which remains after a pet is spayed. We call this a “stump” pyometra. Symptoms will be very similar to a standard pyometra, but the pet may have been spayed many weeks to several years before. 

Causes of Pyometra in Dogs

Starting at approximately 6 months of age, once a pet becomes hormonally mature, a dog will go through a heat cycle every 6 months or so. Each cycle brings the possibility of pregnancy. The uterine lining will thicken in preparation to potentially be the home of a growing embryo. 

In a rare occurrence, the lining continues to thicken abnormally, and cysts form from glands within the wall of the uterus. This abnormal tissue becomes excessive and persistent. It is called cystic endometrial hyperplasia (CEH). 

The exact cause of CEH is not known, but the hormones progesterone and estrogen during successive cycles are definitive factors. Successive cycles means that the likelihood of a dog developing a pyometra increases with each heat cycle that she goes through, as hormonal effects accumulate on the uterus. 

However, pyometras can occur in any reproductively active pet, including dogs that are only 4-6 months old. Once CEH occurs, the engorged uterine tissue is a great breeding ground for an infection. While the uterus is a sterile environment, the vagina is not. Bacteria from the vagina travel into the uterus and become the source of infection for the pyometra. 

The bacteria that most commonly cause pyometras are Escherichia coli (E. coli), staphylococcus, streptococcus, and pseudomonas.

How Veterinarians Diagnose Pyometra in Dogs

When a pyometra is open, the purulent/pustular vaginal discharge makes the diagnosis of a pyometra much easier. When there is no discharge, a diagnosis can be challenging. Your vet may do the following to confirm a diagnosis: 

Blood work: While there is no specific blood test to diagnose a pyometra, blood work tends to be consistent with widespread infection or inflammation. Typically, these pups will have very high levels of white blood cells; however, with dogs that have severe infections, normal or even low white blood cell counts can be possible, as white blood cells leave the blood system and head to the uterus to start fighting on the front lines.  

Elevation in a particular group of blood proteins called globulins can also be seen, as these blood proteins often increase when the immune system is active. Damage to the liver and kidneys may also be seen with severe infections. 

Radiographs or X-rays: Radiographs tend to show an enlarged uterus. The uterus may be grossly swollen, making pyometra easy to diagnose. Other times, it is not as obvious, and confirmation with an ultrasound may be required. 

Ultrasound: An enlarged uterus does not always mean a pyometra; this could also be explained by a pregnancy, hydrometra (fluid distension of the uterus), uterine torsion (twisting of the uterus), or cancer. An abdominal ultrasound can be very helpful to differentiate between a pyometra and other possible conditions. 

Physical exam: Your vet will evaluate your dog with a physical exam and weigh the results of the diagnostic tests to determine the best course of treatment. 

Treatment of Pyometra in Dogs

Surgical removal of the uterus and ovaries, the definitive treatment for a pyometra, removes the source of the hormones and infected uterine tissue. If the ovaries are not removed, they will continue to produce hormones which can affect even the small stump of uterus that is left behind. 

This surgery is much more complex than a routine spay, even though in both surgeries the ovaries and uterus are removed. Once the uterus is infected, it can be quite challenging to remove it safely. 

Many dogs will require intravenous (IV) fluid therapy to help with dehydration and electrolyte abnormalities before surgery can be performed. Antibiotics are generally given during the surgery and continued for 7-14 days after surgery. 

Pain medications are needed after any major surgery, and a pyometra surgery is no exception. Most dogs will most likely need to stay hospitalized for 24-48 hours after surgery for continued care.  

Treatment of a stump pyometra involves removing the infected uterine stump and finding and removing the source of hormones that caused the formation of the stump pyometra in the first place. This may be a small portion of ovary that was left behind after a spay, or, in rare occurrences, a piece of ectopic ovarian tissue, where hormone-producing cells are found outside of the normal ovary locations.  

For breeding animals, there is a medical approach to treating pyometras. However, it is not often recommended, as the success rate is variable. There is considerable risk, and often long-term breeding complications still occur. Please discuss this alternative thoroughly with your veterinary reproductive specialist. 

Recovery and Prevention of Pyometra in Dogs

Prevention is the key to success, as a spay procedure generally keeps a pyometra from ever becoming an issue. If your pet does have surgery for pyometra, surgical recovery at home is similar to that with a spay: 

  • Your pup will need a calm and safe space to stay during recovery. A large kennel or a small room is preferred. 

  • Limit activity to leash walks for elimination purposes only, as any increase in activity can put additional strain on the incision site. 

  • It is very important for your pet to not lick the incision. An e-collar or a surgical suit will help with these recovery efforts. 

  • Check the incision daily for redness, swelling, and/or discharge. 

  • Medications like anti-inflammatories, pain medication, and antibiotics should be given as directed by your vet. 

  • If your dog is not eating or is experiencing lethargy, pain, vomiting, or diarrhea, contact your vet immediately. 

Pyometra in Dogs FAQs

How does pyometra occur?

Hormonal effects in the uterus can cause a buildup of uterine tissue, which can then become infected by bacteria traveling up from the vagina. The uterus fills with an infection, causing the dog to become ill.

When does pyometra occur?

Pyometras can happen in dogs of any age, though it is statistically more likely in an older dog that has not been spayed. One to three months after a dog’s last heat cycle tends to be the time frame in which a pyometra is most likely to occur.

What happens if a pyometra goes untreated?

A closed pyometra can be a life-threatening condition if immediate medical attention is not taken. Even with an open pyometra, the toxic effects from the bacterial infection can be fatal if left untreated.


  1. Veiga, Gisele Almeida Lima, et al. “Cystic Endometrial Hyperplasia-Pyometra Syndrome in Bitches: Identification of Hemodynamic, Inflammatory, and Cell Proliferation Changes.” Biology of Reproduction, vol. 96, no. 1, 1 Jan. 2017, pp. 58–69.  

  2. Merck Veterinary Manual. Pyometra in Small Animals—Reproductive System.  

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Stephanie Howe, DVM


Stephanie Howe, DVM


Dr. Stephanie Howe graduated from the University of Florida College of Veterinary Medicine in 2011, after receiving a Bachelor of Science...

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