Pyometra is a dangerous uterine infection that can have life-threatening consequences if not treated quickly and aggressively. Our Animal Care & Emergency Services team knows how dangerous these infections can be, so we are providing information about pyometra and explaining how you can safeguard your four-legged friend.

What is pyometra?

The word pyometra is derived from the Latin words “pyo,” meaning pus, and “metra,” meaning uterus, so pyometra technically means a pus-filled uterus. The infection causes toxins and bacteria to leak across the uterine wall into the pet’s bloodstream, leading to life-threatening effects throughout the body. 

What causes pyometra in pets?

Several factors contribute to pyometra development in a pet, including:

  • Elevated progesterone levels — Following estrus, progesterone levels remain elevated for several weeks.
  • Thickened uterine wall — The elevated progesterone levels stimulate the uterine wall to engorge in preparation for pregnancy.
  • Cystic endometrial hyperplasia — After several estrus cycles, if pregnancy doesn’t occur, the tissue engorgement becomes excessive or persistent, causing cyst formation, which is called cystic endometrial hyperplasia.
  • Fluid secretion — The thickened cystic lining secretes fluid, creating an ideal environment for bacterial growth. 
  • Static uterine muscles — The elevated progesterone levels also inhibit the uterine wall muscles from contracting and expelling the accumulated fluid and bacteria.
  • White blood cells (WBCs) — During estrus, WBCs are inhibited from entering the uterus to allow sperm to safely enter the female reproductive tract. WBCs typically fight infection, so the inhibition prevents them from combating bacteria that enter the uterus.
  • Relaxed cervix — Typically, the cervix is tightly closed, but the structure relaxes during estrus to allow sperm to enter the uterus. This also allows bacteria to ascend from the vaginal area and enter the uterus. 

Drugs containing estrogen, progesterone, and synthetic estrogen, which are often used to treat reproductive system conditions, can cause uterus changes, increasing the risk for pyometra in these pets. 

When does pyometra typically occur?

Pyometra usually occurs about two to eight weeks after the pet’s last heat cycle. Hormonal effects on the uterine tissue accumulate with every heat cycle, which means that older female pets are at higher risk. 

What are pyometra signs in pets?

Signs depend on whether the pet is affected by closed or open pyometra.

  • Open — In an open pyometra, the cervix remains open, and purulent discharge drains from the uterus and can be seen under the tail and in the pet’s bedding. Affected cats typically fastidiously clean away the discharge, so their owners may not observe any discharge. Other signs, such as fever, lethargy, inappetence, and depression, may or may not be present in a pet with open pyometra.
  • Closed — In a closed pyometra, the cervix is tightly closed, so the purulent discharge can’t drain from the uterus. Affected pets are typically much sicker than those with an open pyometra, because the infection has no outlet and therefore, the toxins that the bacteria release enter the pet’s bloodstream. Signs include fever, depression, inappetence, vomiting, diarrhea, and a distended abdomen.

In open and closed pyometra, toxins released by the bacteria inhibit the kidneys’ ability to retain fluid, resulting in increased urine production, and a compensatory increase in thirst. 

How is pyometra diagnosed in pets?

Pyometra should be suspected in any intact female pet who is sick or has increased thirst and urination. Diagnostics we perform on presentation include:

  • History — Our team asks for information about your pet’s medical history, including their last heat cycle and when signs began.
  • Physical examination — We perform a thorough physical examination, looking for signs such as vaginal discharge and a distended abdomen.
  • Blood work — Our team performs a complete blood count (CBC) and biochemistry profile to assess your pet’s overall health and rule out other conditions. Most affected pets have an elevated WBC, but this does not definitively diagnose pyometra.
  • Urinalysis — The toxic effects of the bacteria on the kidneys cause a low specific gravity in the urine of affected pets, and we may perform a urinalysis. However, this also does not definitively diagnose pyometra.
  • X-rays — In a closed pyometra, X-rays can identify an enlarged, distended uterus.
  • Ultrasound — We may also use ultrasound to evaluate the uterine wall.

How is pyometra treated in pets?

The preferred pyometra treatment is surgical removal of the pet’s uterus and ovaries. However, while spaying a healthy pet is a routine procedure, spaying a pet with pyometra is challenging, especially if the pet is already toxic. Fluid therapy is typically necessary, and antibiotics are needed before and after surgery to combat systemic infection. For pets in stable condition, a medical alternative using prostaglandin treatment is available, but this method isn’t always successful and has serious drawbacks, including:

  • The medication causes side effects, such as restlessness, panting, vomiting, diarrhea, salivation, and abdominal pain that can increase your pet’s distress and discomfort.
  • The medication takes at least 48 hours before improvement occurs, which means that severely ill pets are not good candidates for this treatment.
  • Prostaglandins cause the uterus to contract, and the uterus can rupture in some cases, leading to a severely life-threatening infection called peritonitis. 

Spaying your pet helps prevent the dangerous effects of pyometra. If your intact pet is drinking excessively or exhibiting vaginal discharge, contact our Animal Care & Emergency Services team as quickly as possible, so we can ensure they get the treatment they need.