This article will look at a disease called pyometra, which stems from the Greek meaning “pus in the uterus”. It is a chronic inflammatory disease with an acute manifestation seen predominantly in entire older bitches. Synonyms include purulent endometritis, purulent metritis, pyometritis and chronic cystic endometritis. It can be a life-threatening condition in older, intact bitches and it is therefore important that, if your bitch has not been neutered, a careful record of all her seasons is kept.
Typically, pyometra presents with signs of systemic illness, and so animals are usually presented as depressed, lethargic and anorexic. The signs vary depending on whether the cervix is open or closed. Open cervix pyometra will show vulvar discharge (usually pus-like liquid) while, if the cervix is closed, the bitch may show abdominal distension and more severe signs of depression. Vulvar discharge is the most prevalent sign. The onset of signs may be acute or gradual. Other signs include anorexia, lethargy, vomiting, an increase in the amount of drinking, fever, and even diarrhoea. Sepsis, dehydration, shock and kidney failure can also occur. Pyometra is not usually painful, but if it is, septic peritonitis is likely. This may be due to the uterus rupturing and releasing bacteria into the abdomen.
Signalment and history
Pyometra is usually seen in middle-aged to older bitches. The average age of developing pyometra has been quoted to be between 7.8 and 10 years, with the majority of cases being in animals over six years old.
Breeds that seem to be predisposed include the Golden Retriever, Rough Collie, Rottweiler, Beagle and Cavalier King Charles Spaniel. Animals that have never had a litter are also at an increased risk. Other risk factors include oestrus cycle irregularities, and ovarian diseases.
After your vet has obtained a detailed history and performed a physical exam, they may make a tentative diagnosis of pyometra. Your vet may then advise you that your bitch will need further diagnostic tests such as an ultrasound scan, radiography and a blood sample.
Pyometra has a two-step pathogenesis. Firstly, cystic endometrial hyperplasia (CEH) develops. This is when the cells lining the uterus increase in number due to hormones of the oestrus (or reproductive) cycle. This then predisposes the uterus to a secondary ascending bacterial infection. CEH and pyometra develop during the dioestrus phase of the oestrus cycle. Normally, dioestrus lasts 70 days in a non-pregnant bitch. During dioestrus, the uterus is under the influence of progesterone produced by the ovaries. The progesterone prepares the uterus for pregnancy by promoting glandular development and secretion, as well as increasing the number of cells of the uterine lining. Progesterone also suppresses the uterine immune responses. When endometrial hyperplasia becomes excessive, cysts may form. This is known as CEH. Thus, fluid accumulates within the uterine glands and uterine lumen. When the progesterone level drops at the end of dioestrus part of the oestrus cycle, CEH often regresses. But it may worsen with every subsequent dioestrus cycle. This is how repeated non-pregnant cycles can increase the likelihood of developing CEH as the bitch ages. Oestrogen also has a part to play in this disease process. It produces cervical dilatation during oestrus, allowing bacteria to ascend into the uterus. It also enhances the stimulatory effect of progesterone on the uterus. Normal resident bacteria from the vagina can migrate into the uterus through an open cervix. Escherichia coli (also known as E.coli) is the dominant organism cultured in uterine infections. E.coli is thought to ascend into the uterus from the vagina when the cervix is open during proestrus and oestrus. The strains isolated from the uterus are biologically identical to faecal or bladder urine isolates from the same dog, suggesting faecal contamination. However, this pathogenesis is not accepted by all, as not all bitches with CEH develop pyometra. Some believe it is an age-related disease, while others see the bacterial infection as the primary cause, with incidental CEH. Insulin like growth factor I (IGF-I) may also be involved in the pathogenesis. Studies have shown there to be an increased number of receptors for IGF-I in the uterus of bitches with pyometra.
A Swedish study reported that 23.5 per cent of bitches develop pyometra by 10 years of age if they are not neutered. Pyometra is most commonly seen during the progesterone-dominated phase of the oestrus cycle, that is, within eight weeks of standing heat.
Rarely, we see a condition called stump pyometra in female dogs that have been neutered. This is an inflammation or bacterial infection of a post-ovariohysterectomy remnant of the uterine body or cervix.
Dehydration and septic shock should be treated with intensive intravenous fluid therapy. Broad spectrum antibiotic therapy should be initiated early on to try and control the infection. Ovariohysterectomy (or spay, which is the removal of the ovaries, uterine horns and cervix) is the treatment of choice. Figure four shows a dog undergoing a routine spay, whereas figure five shows a dog being spayed to treat pyometra. In the latter, the horns of the uterus are filled with pus and the uterus is far more vascular when compared to a normal, healthy uterus. Once the uterus is removed the abdomen is closed, and skin sutures will usually stay in place for 14 days before removal. Intensive post-operative care and monitoring for organ failure is vital in order to optimise the recovery process. If left untreated, dogs may subsequently develop septic shock or septicaemia and renal failure. Once the attending vet is happy that the dog is able to go home, the dog is discharged with a 10-14 day course of antibiotics and pain relief. The wound will also have to be carefully checked and monitored, and the use of a buster collar can prevent dogs from licking the wound and pulling out the stitches.
The prognosis is variable, depending on how quickly the diagnosis is made. Sadly, the mortality rate has been quoted to range from four to eight per cent. Death is associated with the systematic complications of pyometra.
The combination of pathogenic bacteria and an abnormal uterine lining leads to pyometra. Pyometra should always be included as a differential diagnosis in a female dog with an acute abdomen or with non-specific clinical signs. This is especially important in the seven to eight weeks following a season. A closed pyometra can be life-threatening and treatment should therefore not be delayed, even if the animal appears healthy. If you are suspicious of this disease in your dog, you should contact your veterinary surgery for an urgent appointment. This disease can be readily prevented by neutering, and careful consideration should be undertaken if you are not intending to breed from your female dogs. Spaying can be done from as early as six months or, if your dog is older, it should be performed three months after a season.