Pyometra is a life-threatening infection of the uterus that occurs most often in intact females over 6 years of age. The disease often begins with a condition called cystic endometrial hyperplasia.
In a dog with cystic endometrial hyperplasia, the inner glandular layer of the uterus becomes thickened, fills with fluid, and forms open pockets like those in Swiss cheese. These endometrial changes are caused by the sustained effect of high levels of progesterone that occur during the 8 to 10 weeks of diestrus. Cystic endometrial hyperplasia provides ideal conditions for bacterial growth. The bacteria gain access to the uterus when the cervix is relaxed during estrus. The subsequent infection leads to pyometra.
A biopsy might detect cystic endometrial hyperplasia, but the condition usually goes unnoticed until it has progressed to pyometra and the bitch becomes ill.
Although estrogen does not cause cystic endometrial hyperplasia, it does increase the effects of progesterone. Estrogen given in the form of a mismate shot to prevent unwanted pregnancy has been associated with a greatly increased risk of pyometra and is no longer recommended for that purpose.
Signs of pyometra appear one to two months after the heat period. A bitch with pyometra appears depressed and lethargic, may refuse to eat, drinks a great deal of water, and urinates frequently. Vomiting and diarrhea also can occur. Her temperature may be normal or even below normal. Suspect pyometra in any intact bitch who appears ill without obvious cause.
There are two types of pyometra: open and closed. In open-cervix pyometra, the cervix relaxes and releases a large amount of pus that often resembles tomato soup. These bitches usually do not appear as ill as those with closed- cervix pyometra.
In closed-cervix pyometra, the undrained uterus enlarges, often producing a painful swelling in the lower abdomen. This type of pyometra is more likely to be accompanied by vomiting and diarrhea, and may produce signs of toxicity such as high fever, rapid pulse, and shock. The diagnosis of closed-cervix pyometra is made by an X-ray of the abdomen showing an enlarged uterus. Ultrasonography distinguishes pyometra from the enlarged uterus of pregnancy; an X-ray taken after about 45 days of pregnancy will also distinguish one from the other.
Treatment: Pyometra requires immediate veterinary attention to prevent shock and death. Ovariohysterectomy, along with antibiotics, is the treatment of choice. It is best to do this operation before the bitch becomes septic.
When it is important to preserve the reproductive potential of a valuable bitch, an alternative to ovariohysterectomy can be considered – provided that the cervix is open and the bitch is not septic. It involves the use of antibiotics along with prostaglandin. Prostaglandin PGF2a (Lutalyse) relaxes the cervix, stimulates uterine contractions, and evacuates the pus. Lutalyse is administered by subcutaneous injection daily for three to five days. If evacuation is not complete, a second course is given. Antibiotics are selected based on sensitivity tests, and are continued for one to three weeks after evacuation of the uterus. Lutalyse is not licensed by the FDA for use in small animals, but is nevertheless widely used for this purpose.
Prostaglandin treatment is accompanied by a number of dose-related side effects, including shock. Uterine rupture may occur when the cervix is closed. Most veterinarians regard closed-cervix pyometra as a contraindication to the use of Lutalyse.
Bitches who recover from pyometra are at increased risk for developing it again on subsequent heat cycles. They should be bred on the first estrus after recovery to maximize their chances for fertility.