Pyometra -what is it?

Pyometra is an infection in the uterus. This is a life-threatening infection – toxins and bacteria leak across the uterine walls and into the bloodstream, and without treatment the infection results in a severe, usually fatal, septicaemia. Pyometra occurs in female dogs and cats.

How does the infection occur?
During a heat cycle, hormones cause the uterine lining to engorge and thicken in preparation for pregnancy and if pregnancy doesn’t occur, the hormone levels drop and the uterus reverts to its neutral state. Over time, some of the uterine tissue engorgement becomes persistent (a condition called cystic endometrial hyperplasia). This thickened glandular uterine tissue provides the ideal environment for bacteria to grow.

Pyometra is more common in older pets because they have experienced more heat cycles and hence are more likely to have the uterine wall changes that are supportive of infection but it can occur as early as 2-3 years of age.

The uterus is normally sterile. During a heat cycle, hormones cause the cervix to open to allow sperm to enter the uterus. During this time, bacteria that normally live in the vagina can also migrate through the cervix and enter the uterus. If the uterus is normal, the bacteria usually do not survive. If the uterine wall is thickened and cystic the bacteria can colonize and start to multiply resulting in pus formation. In addition to this, hormones during the heat cycle and the abnormal uterine wall prevent the muscle of the uterus from contracting so the pus cannot be evacuated effectively.

Pyometra normally develops 2-8 weeks after a heat cycle. The signs depend on whether the cervix is open or closed.

What are the signs of pyometra?
Signs include a poor appetite, lethargy, depression, increased thirst and urination, there may be abdominal distension, vomiting and /or diarrhoea. In “open pyometra,” as the cervix is open, a smelly vaginal discharge is usually apparent. Whereas in “closed pyometra”, there is no vaginal discharge and the pet tends to be sicker because more pus and toxins accumulate. Cats can be more difficult to diagnose than dogs as they often keep eating until very late in the disease, they groom away any vaginal discharge quickly (delaying owners notice) and the owner often thinks they are pregnant due to their distended belly.

How is pyometra diagnosed?
Diagnosis requires a history of an intact female who has been on heat within the last 2-3 months. For those with an open pyometra diagnosis can be simple but in closed pyometra blood tests, x-rays or an ultrasound are usually required.

What is the treatment for pyometra?
The usual treatment for pyometra is surgical removal of the infected uterus and ovaries (desex or spay) and treating the septicaemia with iv fluids and antibiotics. Performing surgery on a sick septic pet is challenging and not without significant risks.

There is an alternative, often more expensive, medical treatment. It involves hospitalisation and using hormones to open the cervix and contract the uterus to expel the pus. Treatment is not always successful especially in closed pyometra cases. The disease is resolved more slowly and there is a risk of uterine rupture and life-threatening peritonitis. They must be bred and get pregnant on the next heat cycle otherwise the risk of pyometra recurrence is high (50-70%). The chance of a successful future pregnancy is reduced due to the permanent uterine changes so unless the pet has great value to a breeding program it might not be worth attempting medical treatment.

How do I prevent my pet from getting pyometra?
Spaying otherwise called desexing (surgical removal of the ovaries and uterus) prevents this disease. Often owners have plans to breed a pet or are undecided, time passes, and then they fear their pet is too old to be spayed but any perceived risks of surgery are very much out-weighed by the risk of pyometra.

The best approach is to be aware that pyometra is highly likely to occur if the female pet is left unspayed; once you have finished breeding or if you have no plans to breed and your pet is 5-6 years old then get her desexed whilst she is healthy (or at least watch her very closely for signs of infection after every heat).