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Pyometra and Cystic Endometrial Hyperplasia in Dogs

What Is Pyometra in Dogs?

Pyometra in dogs is a serious bacterial infection within the reproductive tract, leading to the accumulation of purulent material in the uterus. This condition arises due to hormonal fluctuations in female dogs. While cystic endometrial hyperplasia is often used interchangeably with pyometra, they aren’t precisely the same. Cystic endometrial hyperplasia involves thickening of uterine tissue, creating an optimal environment for pyometra development.

The bacterial infection can result in toxins seeping through the uterine wall into the bloodstream, triggering a systemic infection known as sepsis. The uterus becomes fragile, potentially leading to pus leakage into the abdomen. Without prompt intervention, pyometra can pose life-threatening consequences for affected dogs.

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Uncertain whether your pet needs veterinary attention? Answer a few questions regarding your pet’s symptoms, and our vet-designed Symptom Checker will provide you with the most probable causes and recommended next steps.

Symptoms and Types

Symptoms of pyometra in dogs can be elusive and may mimic other infectious diseases. Typically, veterinarians suspect pyometra in a dog that has recently completed her heat cycle, around 1-2 months earlier, and exhibits one or more of the following symptoms:

  • Pustular to bloody vaginal discharge
  • Decreased appetite
  • Vomiting or diarrhea
  • Increased water intake
  • Lethargy or depression
  • Fever

In cases of “open” pyometra, where the cervix is open, infectious material from the uterus leaks out through the vagina or vulva. Owners may observe a small to moderate amount of discharge on the pet’s vulva, tail, bedding, or resting areas.

However, pyometra can also manifest with a closed cervix, making diagnosis more challenging as no discharge can escape the uterus. Dogs with closed cervix pyometra often present with more severe symptoms since the infection is trapped inside the body.

While pyometra primarily affects non-spayed females, there are rare instances of uterine tissue infection persisting after spaying, known as “stump” pyometra. Symptoms resemble those of standard pyometra, but the pet may have been spayed weeks to several years prior.


Pyometra in dogs typically stems from the hormonal maturity reached around 6 months of age, initiating heat cycles occurring approximately every 6 months. During each cycle, the uterine lining thickens in anticipation of potential embryo implantation.

In rare instances, the uterine lining thickens excessively, forming cysts from glands within the uterine wall, a condition known as cystic endometrial hyperplasia (CEH). While the precise cause of CEH remains unknown, hormones like progesterone and estrogen play crucial roles in its development. With successive heat cycles, the likelihood of developing pyometra increases as hormonal effects accumulate on the uterus.

Despite being primarily associated with mature dogs, pyometras can also affect reproductively active pets as young as 4-6 months old. Once CEH develops, the engorged uterine tissue becomes an ideal breeding ground for infections. Although the uterus is typically sterile, bacteria from the vagina can infiltrate and trigger the infection underlying pyometra.

Common bacterial culprits responsible for pyometras include Escherichia coli (E. coli), staphylococcus, streptococcus, and pseudomonas.


Diagnosing pyometra in dogs can vary depending on whether the condition presents with purulent vaginal discharge or not. When discharge is absent, diagnosis becomes more challenging. Here’s how veterinarians typically confirm a pyometra diagnosis:

Blood work: Although there isn’t a specific blood test for pyometra, blood work often reveals signs of widespread infection or inflammation. Dogs with pyometra usually exhibit elevated white blood cell counts, although in severe infections, white blood cell counts can be normal or even low as cells migrate to the uterus to combat the infection. Additionally, an increase in globulins, a group of blood proteins, may indicate heightened immune activity. Damage to the liver and kidneys may also be evident in severe cases.

Radiographs or X-rays: Enlargement of the uterus is often visible on radiographs, aiding in the diagnosis of pyometra. However, in some cases, the enlargement may not be obvious, necessitating confirmation through ultrasound imaging.

Ultrasound: While an enlarged uterus could signify pyometra, it could also indicate pregnancy, hydrometra (fluid distension), uterine torsion, or cancer. Abdominal ultrasound is valuable in distinguishing pyometra from other conditions.

Physical exam: Veterinarians conduct a thorough physical examination to assess the dog’s condition and interpret the results of diagnostic tests, guiding the selection of the most appropriate treatment plan.


The primary treatment for pyometra in dogs involves surgical removal of the uterus and ovaries, eliminating the source of hormones and infected uterine tissue. If the ovaries are not removed, hormone production may persist and affect any remaining uterine stump. This surgery is more complex than a routine spaying procedure since the infected uterus poses challenges for safe removal.

Before surgery, many dogs require intravenous (IV) fluid therapy to address dehydration and electrolyte imbalances. Antibiotics are administered during and after surgery for 7-14 days to combat infection. Post-surgery, pain medications are essential, and most dogs need hospitalization for 24-48 hours for ongoing care.

Treatment of stump pyometra involves removing the infected uterine stump and identifying the source of hormones that led to its formation. This may involve removing residual ovarian tissue left after spaying or, in rare cases, ectopic ovarian tissue containing hormone-producing cells outside the normal ovary locations.

For breeding animals, a medical approach to treating pyometras exists but is generally not recommended due to variable success rates and considerable risks. Long-term breeding complications may still occur. Owners should thoroughly discuss this alternative with a veterinary reproductive specialist.

Recovery and Prevention

Preventing pyometra in dogs is best achieved through spaying, which eliminates the risk of this condition. In case your pet undergoes surgery for pyometra, the recovery process at home resembles that of a spay:

  • Provide a calm and secure environment for your pet’s recovery, preferably in a spacious kennel or a confined room.
  • Restrict activity to leash walks only for toileting purposes to avoid strain on the incision site.
  • Prevent licking of the incision by using an e-collar or surgical suit.
  • Monitor the incision daily for signs of inflammation, swelling, or discharge.
  • Administer medications such as anti-inflammatories, pain relievers, and antibiotics as prescribed by your veterinarian.
  • Contact your vet immediately if your dog shows signs of decreased appetite, lethargy, pain, vomiting, or diarrhea during the recovery period.

Pyometra in Dogs FAQs

How does pyometra occur?

Pyometra can develop due to hormonal changes in the uterus, leading to the accumulation of uterine tissue that becomes susceptible to bacterial infection from the vagina. The infected uterus results in illness in the dog.

When does pyometra typically occur?

Pyometra can occur in dogs of any age, but it’s more commonly observed in older, unspayed dogs. The period of one to three months after a dog’s last heat cycle is when pyometra is most likely to manifest.

What are the consequences of untreated pyometra?

Untreated pyometra, whether open or closed, can pose life-threatening risks. In the case of a closed pyometra, immediate medical attention is crucial to prevent fatalities. Even with an open pyometra, the toxic effects of the bacterial infection can lead to fatal outcomes if left untreated.

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