Pyometra, meaning "pus-filled uterus," is a life-threatening infection of the uterus that affects female dogs. It’s most common in unspayed dogs older than 6, and the condition is a medical emergency.
The disease starts with cystic endometrial hyperplasia, a condition in which the uterine lining thickens and forms cysts in response to the hormone progesterone. In this abnormal condition, the uterus is susceptible to infection from bacteria that enter through the open cervix during the heat cycle.
Risk factors and detection
Any unspayed female dog is at risk for pyometra. Infection occurs most often in middle-aged dogs. Symptoms usually appear four to six weeks after your dog’s heat cycle, but this can vary. The use of a "mismate" shot (administered after breeding to prevent pregnancy) also increases the risk. If an unspayed female appears ill without obvious cause, there’s a good chance she’s developed pyometra.
Pyometra occurs in one of two forms: open or closed. In a closed pyometra, the cervix remains closed, so the pus cannot drain from the uterus. In an open pyometra, the cervix is open enough to allow drainage, and you may notice discharge from the vulva. This discharge is thick and varies in color from cream to pink to brown—it often looks like tomato soup.
Signs of pyometra include lethargy, appetite loss, fever, abdominal enlargement, vomiting, and increased thirst and urination. If the cervix is open and the pus can drain, the symptoms are often less severe. However, this infection can quickly cause serious illness, including a high fever, rapid pulse, and shock, especially with a closed pyometra. So take your dog to the veterinarian immediately if you suspect infection.
Your veterinarian can detect pyometra with an abdominal X-ray or ultrasound. Both detect an enlarged uterus, and an ultrasound can distinguish between pyometra and the enlarged uterus of pregnancy. Blood tests, especially a white blood cell count, also can indicate infection and help your veterinarian assess the severity of the condition.
Prevention and treatment
The best way to prevent pyometra is to spay female dogs who aren’t being used for breeding. This also prevents unplanned pregnancies and may help prevent mammary cancer.
If your dog is a valuable breeding animal, medical treatment is sometimes an option. Medical treatment includes injections of prostaglandin, a hormone that causes the uterus to contract and expel the infected contents. Your veterinarian will administer the injections over three to five days. If evacuation isn’t complete, the doctor may recommend a second course of treatment with prostaglandin, and your dog will need antibiotics for one to three weeks after evacuation of the uterus. This treatment isn’t recommended for a closed pyometra because contractions against a closed cervix could rupture the uterus. And prostaglandin treatment can have adverse side effects, including shock. Medical therapy is also not recommended for critically ill patients, who need immediate removal of the infected uterus to survive.
If your dog is treated medically and recovers, breed her at the next heat cycle, because pyometra often recurs. The underlying cystic endometrial hyperplasia also will limit her fertility, so it’s best to have the desired litters as soon as possible, then spay her to prevent recurring disease.
For most pyometra cases, the treatment is immediate surgical removal of the infected uterus and the ovaries, called an ovariohysterectomy. Performing surgery on a critically ill dog is risky, but surgery is the only lifesaving treatment for these dogs. Your doctor will administer antibiotics to treat infection and intravenous fluids to correct dehydration and shock. The bottom line: Do yourself and your dog a big favor by spaying her to avoid this emergency.
