Diagnosis

Dogs that are seen early in the disease may have a slight vaginal discharge and show no other signs of illness. Most dogs with pyometra are not seen until later in the illness. A very ill female dog that is drinking an increased amount of water and has not been spayed is always suspected of having pyometra. This is especially true if there is a vaginal discharge or an enlarged abdomen.

Dogs with pyometra have a marked elevation of the white blood cell count and often have an elevation of globulins (a type of protein produced by the immune system) in the blood. The specific gravity of the urine is very low due to the toxic effects of the bacteria on the kidneys. All of these abnormalities may be present in any dog with a major bacterial infection.

If the cervix is closed, radiographs (x-rays) of the abdomen will often identify the enlarged uterus. If the cervix is open, there will often be such minimal uterine enlargement that the radiograph will not be conclusive. An ultrasound examination can also be helpful in identifying an enlarged uterus and differentiating that from a normal pregnancy.

Causes

There appears to be a correlation between pyometra and the administration of hormones such as estrogen and progesterone. In the presence of high concentrations of progesterone, as would be seen in a normal canine cycle or the administration of a mis-mating shot, with estrogen seems to have a correlation with pyometra in dogs older than 4 years of age. Administration of progesterones has not been shown to increase the risk of developing pyometra; however, we know that in the normal uterine environment, progesterone is potentially the hormone that sets the uterus up for infection if bacteria become involved.

If bacteria enters the uterus at the times when the protective physical barriers are breached, such as estrus, parturition, or immediately after parturition, the normal uterine defense mechanisms are likely to eliminate these bacteria. However, the hormonal influences may not allow the body to clear the bacteria. The bacteria typically cultured from the pyometra are bacteria that would be found in the areas of the intestines and vagina (E coli is the most common). Therefore, many of the infections are considered either from an ascending infection from the vagina, a concurrent urinary tract infection or fecal contamination. Certain bacteria are more virulent than others and therefore allow a bacterium that is normally found on the dog to develop into an infection.