What is pyometra?
Pyometra is a serious and life-threatening infection in the uterus that must be treated quickly and aggressively. It develops due to normal hormonal changes after a female dog’s heat cycle.
How does pyometra develop?
It is believed that elevated levels of progesterone are involved in the development of pyometra, although this process is not completely understood. After estrus (heat), progesterone levels are higher than normal to initiate thickening of the uterine lining in preparation for pregnancy. Prolonged, elevated progesterone can result in abnormal thickening of the uterine lining and cysts may form in the uterus.
The thickened cystic lining secretes fluids, creating an ideal environment for bacteria. At the same time, the muscles of the uterus cannot contract properly due to the thickening of the uterine wall, so the uterus cannot easily expel accumulated fluids or bacteria.
Normally, the body’s white blood cells would attack any infection, but during estrus, the uterus keeps white blood cells out so that sperm can safely enter the female's reproductive tract without being damaged or destroyed. The absence of white blood cells may allow the bacterial infection to grow unimpeded.
Progesterone-based drugs can cause changes in the uterus similar to the estrous cycle. In addition, estrogen or synthetic estrogen drugs increase the effects of progesterone on the uterus. Drugs that contain both estrogen and progesterone are used to treat certain conditions of the reproductive system. Any intact female dog that receives hormones must be carefully monitored for the development of pyometra.
How do bacteria get into the uterus?
The cervix is the gateway to the uterus. Most of the time, it is tightly closed, but during estrus it relaxes to allow sperm to enter the uterus. When the cervix is open or relaxed, bacteria normally found in the vagina can easily enter the uterus. If the uterine wall is thickened or cystic, the conditions are perfect for bacterial growth.
When does pyometra occur?
Pyometra may occur in any sexually intact young to middle-aged dog, but it is most common in older dogs. After many years of estrous cycles without pregnancy, the uterine wall undergoes changes that promote this disease. Typically, the dog has been in heat within the previous four to six weeks, but pyometra can occur two to sixteen weeks after the last heat cycle.
What are the clinical signs of pyometra?
The clinical signs of pyometra depend on whether the cervix remains open.
Open pyometra: If the cervix is open, purulent discharge (pus) will drain from the uterus through the vagina to the outside. This discharge may be observed on the skin or hair under the tail or on bedding and furniture where the dog has recently laid. With an open pyometra, fever, lethargy, anorexia, and depression may or may not be present.
Closed pyometra: If the cervix is closed, discharge cannot drain to the outside, so it collects in the uterus, causing distention of the abdomen (swollen belly). The bacteria release toxins that are absorbed into the circulation. Dogs with closed pyometra become severely ill very quickly. They are anorectic (will not eat), listless, and depressed. Vomiting or diarrhea may also be present.
In both open and closed pyometra, toxins released by the bacteria affect the kidney's ability to retain fluid. Increased urine production occurs, and the dog drinks large amounts of water to compensate.
How is pyometra diagnosed?
Dogs in the early stages of pyometra may only have a small amount of vaginal discharge and show no other signs of illness. However, most dogs are diagnosed later in the illness. Any very ill female dog that is drinking an increased amount of water and has not been spayed should be suspected of having pyometra, particularly if there is a vaginal discharge or a painful, enlarged abdomen.
Your veterinarian will use a combination of tests to make the diagnosis:
Blood tests usually show a severe elevation in the white blood cell count. Other changes may also be seen, but these are not specific to pyometra and can occur with other serious infections (e.g., high levels of globulins—a protein often associated with the immune system).
Urine tests may show that the urine is more diluted than normal, which can happen due to the toxic effects of the bacteria on the kidneys.
Imaging (X-rays or ultrasound) may be used to look at the uterus:
- If the cervix is closed, radiographs (X-rays) of the abdomen often show an enlarged uterus.
- If the cervix is open, the uterus may not look enlarged on X-rays.
- Ultrasound examination may help identify an enlarged, fluid-filled uterus and distinguish it from a normal pregnancy.
How is pyometra treated?
The preferred treatment for pyometra is to surgically remove the uterus and ovaries by performing an ovariohysterectomy (spay). However, pyometra surgery is more complex than a routine spay because the uterus is much larger and more fragile. Dogs diagnosed in the early stage of the disease are good candidates for surgery. Dogs diagnosed later in the disease are at higher risk for anesthetic complication and death and require treatment for sepsis/peritonitis after the surgery. Intravenous fluids are required to stabilize the dog before and after surgery.
Most dogs require intravenous fluids before and after surgery to help stabilize them. Antibiotics are also given, usually starting before surgery and continuing for two weeks after surgery.
I want to breed my dog in the future. Is there an alternative to surgery?
For most dogs with pyometra, surgery (spaying) is the safest and most effective treatment, and is strongly recommended. A medical approach to treating pyometra can be considered; however, this option is less reliable and carries considerable risks and potential long-term complications.
Medical treatment for pyometra uses prostaglandins. Prostaglandins are hormones that lower levels of progesterone in the blood, open the cervix, and cause the uterus to contract to push out bacteria and pus. The treatment is not always successful and it has some important limitations.
- Side effects: Dogs often feel quite unwell after treatment. Side effects can include restlessness, panting, vomiting, defecation, salivation, and abdominal pain. These usually start about 15 minutes after administration and may last a few hours, although they tend to lessen with repeated doses.
- Slow to work: It takes about 48 hours before clinical improvement to be seen, so it is not a good option for severely ill dogs that need immediate care.
- Risk of uterine rupture: As the uterus contracts, there is a risk it could tear (rupture) and leak infection into the abdominal cavity, resulting in a life-threatening condition known as peritonitis. . This risk is higher if the cervix is closed.
- High chance of recurrence: Even if treatment is successful, the uterus is still abnormal, so pyometra often comes back and future fertility will be compromised.
Your veterinarian will help you decide the best course of treatment depending on your dog’s needs.
What happens if pyometra is not treated?
If pyometra is not quickly treated with surgery or prostaglandins, the toxic effects from the bacteria are fatal in many cases. If the cervix is closed, the uterus can rupture, spilling the infection into the abdominal cavity, which will be fatal. Pyometra is a serious medical condition that requires prompt treatment.
