Canine Pyometra

What is pyometra?

Pyometra means infection of the uterus, the organ in which the young develop during pregnancy. (In women the uterus is sometimes referred to as the womb.) Pyometra in dogs can be a serious, even life-threatening condition. Depending on the severity of the infection, the dog may appear healthy, be slightly off, or be desperately ill from absorption of bacterial toxins into the bloodstream.

What causes pyometra?

The infection is caused by bacteria that enter the uterus from the vagina. When the dog is in estrus ("heat"), her cervix (the passage between the vagina and the uterus) relaxes and opens a little. This relaxation can be sufficient to allow bacteria in the vagina to enter the uterus. For the rest of the dog's heat cycle, the cervix remains tightly closed, forming a barrier between the uterus and the outside.

Ordinarily, the uterus has some potent defense mechanisms for limiting bacterial invasion and bacterial growth. They include the local immune response with antibodies and white blood cells; production of fluid by the lining of the uterus; and contraction of the uterus to expel any fluid, bacteria, and cellular debris through the cervix. Pyometra can develop when these defense mechanisms are compromised.

In dogs, the key factor in the development of pyometra is hormonal changes. In the weeks following the heat or estrus period, elevated levels of a hormone called progesterone cause the lining of the uterus to thicken. This is an appropriate response if the dog is pregnant. If pregnancy does not occur, the uterine lining may continue to increase in thickness over several estrous cycles. During estrus the uterus produces mucus-like fluid that is an ideal environment for bacteria to grow in. At the same time, high progesterone levels relax the uterus and interfere with its ability to contract and expel any fluid and debris that has accumulated.

These changes can occur spontaneously. They can also develop when progesterone-like drugs are used to suppress estrus or treat certain reproductive conditions. Estrogen can increase the sensitivity of the uterus to progesterone, so medications containing both hormones can further increase the potential for pyometra to develop. Pyometra can occur in young and middle-aged dogs. Because it takes some time for the changes in the uterine lining to develop, pyometra is most commonly seen in older dogs.

What are the signs of pyometra?

Pyometra can develop at any stage of the estrous cycle, although it is more common 1-2 months after estrus. The signs depend on whether the cervix is open or closed. If the cervix is open, any infected material (pus) can drain freely from the uterus. In these "open" pyometras, you may see a white or brownish discharge coming from the vulva or sticking to the hairs below the vulva or on the underside of the tail. You may also notice soiling of the bedding or furniture where the dog has rested. Other signs that may be present include loss of appetite, lethargy, and fever. However, some dogs with open pyometra appear healthy, except for the discharge.

If the cervix is closed, the pus builds up within the uterus. In small or thin dogs, the enlarged uterus may cause obvious swelling of the abdomen. As the uterus cannot expel the pus through the cervix, bacterial toxins build up and are absorbed into the bloodstream. As a result, dogs with "closed" pyometra can quickly become ill. Signs include loss of appetite, severe depression, weakness, and in some cases vomiting or diarrhea. The bacterial toxins can affect the kidneys, so dogs with pyometra may drink more water and urinate more than normal.

How is pyometra diagnosed?

Diagnosing pyometra needs to be done by your veterinarian. In most cases the veterinarian suspects pyometra from the signs and the fact that the patient is a female that has not been spayed. In many cases of closed pyometra, it is possible for the veterinarian to feel the enlarged uterus while gently palpating the abdomen. If there is any doubt, the veterinarian may recommend laboratory tests and X Rays. Abnormalities often include a high white blood cell count and globulin level, and very dilute urine. However, these abnormalities are not specific for pyometra; they can occur with any severe bacterial infection.

With closed pyometra, the enlarged uterus is often visible on radiographs (x-ray films), which can aid diagnosis. An ultrasound examination can also be useful in identifying enlargement of the uterus and differentiating pus/fluid accumulation from pregnancy.

How is pyometra treated?

The recommended treatment for pyometra is surgical removal of the infected uterus. The ovaries are removed at the same time. This procedure is called an ovariohysterectomy (commonly referred to as a spay). The surgical procedure is more involved than a routine spay. Most dogs with pyometra are quite ill by the time the condition is diagnosed, so the veterinary surgeon will take extra precautions. Intravenous fluids may be given before, during, and after surgery, and the dog may have to remain hospitalized for several days. Antibiotics are given for 1-2 weeks. In most cases the prognosis for survival is very good with prompt and appropriate treatment. Osteoporosis and other hormone-associated problems that can develop in women after removal of the ovaries do not seem to be a problem in dogs.

Is there an alternative to spaying?

In some cases, such as a valuable breeding dog with an open pyometra, the condition can be treated medically. Medical treatment involves using prostaglandin to contract the uterus and expel the infected material through the cervix. This approach is not always successful, and it can have some serious drawbacks. The outcome with medical treatment depends on whether the cervix is open or closed. Open pyometra has a higher success rate with medical treatment, whereas the success rate for closed pyometra is low. Also important to note is that there is a good chance of recurrence with medical treatment. The chance of successful breeding following treatment is only 50-75%. Your veterinarian can advise you which method of treatment is best for your pet.

by William M. Fraser, D.V.M.

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