What is pyometra?
In its simplest terms, pyometra is an infection in the uterus. However, most cases of pyometra are much more difficult to manage than a routine infection.
Infection in the lining of the uterus is established as a result of hormonal changes. Following oestrus (“heat”), progesterone levels remain elevated for 8-10 weeks and thicken the lining of the uterus in preparation for pregnancy. If pregnancy does not occur for several oestrus cycles, the lining continues to increase in thickness until cysts form within it. The thickened, cystic lining secretes fluids that create an ideal environment in which bacteria can grow. Additionally, high progesterone levels inhibit the ability of the muscles in the wall of the uterus to contract.
Are there other situations that cause the changes in the uterus?
Yes. The use of progesterone-based drugs can do this. In addition, oestrogen will increase the effects of progesterone on the uterus. Drugs containing both hormones are used to treat certain conditions of the reproductive system.
How do bacteria get into the uterus?
The cervix is the gateway to the uterus. It remains tightly closed except during oestrus. When it is open, bacteria that are normally found in the vagina can enter the uterus rather easily. If the uterus is normal, the environment is adverse to bacterial survival; however, when the uterine wall is thickened and cystic, perfect conditions exist for bacterial growth. In addition, when these abnormal conditions exist, the muscles of the uterus cannot contract properly. This means that bacteria that enter the uterus cannot be expelled.
When does it occur?
Pyometra may occur in young to middle-aged dogs; however, it is most common in older dogs. After many years of oestrus cycles without pregnancy, the uterine wall undergoes the changes that promote this disease.
The typical time for pyometra to occur is about 1-2 months following oestrus.
What are the clinical signs of a dog with pyometra?
The clinical signs depend on whether or not the cervix is open. If it is open, pus will drain from the uterus through the vagina to the outside. It is often noted on the skin or hair under the tail or on bedding and furniture where the dog has laid. Fever, lethargy, anorexia, and depression may or may not be present.
If the cervix is closed, pus that forms is not able to drain to the outside. It collects in the uterus causing distension of the abdomen. The bacteria release toxins which are absorbed into the circulation These dogs often become severely ill very rapidly. They are anorectic, very listless, and very depressed. Vomiting or diarrhoea may be present. Toxins from the bacteria affect the kidney’s ability to retain fluid. Increased urine production occurs, and the dog drinks an excess of water. This occurs in both open- and closed-cervix pyometra.
How is it diagnosed?
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. However, 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.
How is it treated?
The preferred treatment is to surgically remove the uterus and ovaries. This is called an ovariohysterectomy (“spay”). However, these dogs are quite ill so the surgery is not as routine as the same surgery in a healthy dog. Intravenous fluids are often needed before and after surgery. Antibiotics are given for 1-2 weeks.
What happens if treatment is not given?
The chance of successful treatment without surgery is extremely low. If treatment is not performed quickly, the toxic effects from the bacteria will be fatal. If the cervix is closed, it is also possible for the uterus to rupture, spilling the infection into the abdominal cavity. This will also be fatal.