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Understanding Pyometra in Female Dogs

 

By Ivana Crnec DVM

Pyometra in female dogs is a common reproductive disorder consisting of the accumulation of purulent secretions (producing pus) which take place in the uterine lumen of female dogs. This conditions tends to occur during or immediately following a period of progesterone dominance, which may take place anywhere between 4 weeks to 4 months following a dog’s estrus (the part of the heat cycle when the dog is ready to mate and fertile). Canine pyometra may fall into two different classifications: open cervix (also known as open pyometra) or close cervix pyometra (also known as closed pyometra).

Pyometra affects intact (nonspayed female dogs)

Facts About Pyometra 

It’s an unfortunate fact that pyometra is a very common condition and despite the institution of modern treatment, the mortality rate  from this condition is about 4 percent.

Pyometra usually occurs in older females (dogs who are older than 6 years of age) as a result of repeated endometrial exposure to the hormones estrogen and progesterone.

Nulliparity (the condition of never haven given birth), abnormal heat cycles, false pregnancy and hormonal therapies (such as mismate injections) increase a dog’s risk for pyometra.

Belonging to certain dog breeds can be another trigger. Breeds reported to be predisposed to pyometra include the Irish Terrier, Chow Chow, Bernese Mountain Dog, Rottweiler, Rough-haired Collie, Cavalier King Charles Spaniel and Golden Retriever.

On the other hand, breeds with low risks for pyometra include German Shepherd, Daschund and Swedish Hound.




How Dogs Get Pyometra

Enlarged uterus in dog filled with pus

Canine pyometra is a pathological process that takes place in two phases. The first pathologic change is what’s known as  cystic endometrial hyperplasia (CEH) which is the thickening of the dog’s uterine lining due to repeated heat cycles. High levels of serum estrogen followed by prolonged elevation in progesterone after every cycle, promote hyper-reactivity of the lining of the uterus and gradual cystic hyperplasia.

The second pathologic change is infection. Anatomically, the dog’s cervix is the gateway to the uterus. The dog’s cervix normally remains tightly closed except during estrus (the part of the heat cycle when the dog is ready to mate and fertile), when it relaxes so to allow sperm to enter the uterus.

If the cervix is either open or relaxed, then bacteria from the vagina have a chance to easily enter the uterus. In normal physiological conditions, the uterine environment does not support bacterial survival. However, when there is a thickened or cystic uterine wall, it creates the perfect condition for bacteria to grow and thrive.

In addition, because of the wall being thickened or the influence of progesterone, the muscles of the uterus cannot properly contract which means that the bacteria that entered the uterus cannot be expelled.

Lethargy in any intact female dog should be investigated.

Symptoms of Pyometra in Dogs

The main problem with pyometra is that the onset of clinical signs is gradual and insidious. The clinical signs vary, depending on patency (the condition of being open) of the cervix.

In cases of open pyometra, pus or abnormal discharge drains from the uterus through the vulva. The discharge is yellow-green to pink or red-tinged, thick and odoriferous (giving off a smell). Such discharge may often be recognized by dog owners as it accumulates on the skin or hair under the dog’s tail or on bedding and furniture where the dog has recently laid.

Affected dogs can be either febrile (have fever) or hypothermic (having low body temperature). Loss of appetite, increased water intake, increased urination and depression may or may not be present.

In cases of closed pyometra, the discharge accumulates in the uterus ultimately causing abdominal distension (expansion of the abdomen). Because the bacterial toxins enter the bloodstream, dogs become ill rapidly. The systemic signs of the disease are same as with open cervix pyometra, but usually they tend to be more severe.

At the Vet’s Office 

Surgery is the gold standard treatment for pyometra in dogs.

Diagnosis of pyometra can be obtained when there is demonstration of excessive fluid in the uterus or purulent vulvar discharge in the case of open pyometra.

If the cervix is closed, signs of infection are necessary for diagnosing. Uterine enlargement can be identified by abdominal palpation, x-rays and by ultrasound. Cytology of the discharge reveals full fields of bacteria, degenerative polymorphonuclear cells and non-cornified epithelial cells. Bloodwork shows leukocytosis  (an increase in the total number of white blood cells) with a left shift, while the urine analysis shows decreased specific gravity and proteinuria (presence of proteins).

Pyometra in female dogs is a serious and life threatening, medical emergency that requires rapid and aggressive intervention. Without treatment, the infection can turn quickly fatal. During the last decade, numerous treatments have been proposed to treat both open and closed cervix pyometra. All treatments can be categorized in two groups – medical and surgical.

Medical treatment of pyometra may only be considered in cases of open pyometra and if the symptoms are mild, but medicines cannot guarantee positive outcome. Even if the present outcome is positive, future management of the estrous cycles are required.

The treatment of choice when it comes to pyometra is ovariohysterectomy (complete removal of the uterus and ovaries). The main advantage of surgical over medical management is that it is curative and prevents future occurrences.




The Bottom Line

As the dog’s uterus ages, it is prone to changes. The changes that lead to pyometra are among those changes. Therefore most intact female dogs, presuming they live long enough, can eventually develop pyometra. It is for this reason, that it is recommended spaying any female dog, who is not being actively used for breeding.

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