Pyometra
Pyometra
Also known as: CEH-pyometra, Closed-cervix pyometra, Open-cervix pyometra
CatDogUrgency: Emergency
Pyometra
Also known as: CEH-pyometra, Closed-cervix pyometra, Open-cervix pyometra
In short
Pyometra is a severe, life-threatening uterine infection affecting unspayed dogs and cats. Recognizing symptoms like vaginal discharge, increased thirst, and lethargy early is critical, as emergency surgery is often required to save the animal's life.
TL;DR. Pyometra is a life-threatening uterine infection in unspayed dogs and cats that requires emergency veterinary intervention, typically involving surgical removal of the uterus.
Pyometra causes the uterus to become severely distended and filled with toxic, infected fluid.
Pyometra is one of the most common and dangerous reproductive emergencies seen in veterinary medicine. It is a severe, acute, or chronic bacterial infection of the uterus that primarily affects intact (unspayed) female dogs and cats. The name itself comes from the Latin words for pus ("pyo") and uterus ("metra"). This condition is classified as a septic inflammatory disease, meaning it triggers a massive immune response alongside a localized, highly toxic infection.
To understand why pyometra occurs, we must look at the hormonal cycle of female pets. Unlike humans, dogs and cats experience a unique reproductive cycle driven by the hormone progesterone. After a female pet goes through estrus (heat), her body enters a phase called diestrus, which lasts for approximately two months. During this time, the ovaries produce high levels of progesterone, regardless of whether she is pregnant or not.
Progesterone prepares the uterus for potential pregnancy by thickening the uterine lining (endometrium), increasing glandular secretions, and reducing the natural muscular contractions of the uterus. While these changes are necessary to support developing embryos, they also create a perfect environment for bacterial growth. If a pet goes through multiple heat cycles without becoming pregnant, the chronic exposure to progesterone can cause the uterine lining to become abnormally thick and cystic—a condition known as cystic endometrial hyperplasia (CEH).
As a leading veterinary critical care textbook explains:
"Pyometra often is preceded by CEH but can develop independently of CEH. It is an endocrine disease occurring during diestrus, when corpora lutea are present and serum progesterone concentratio" [5]
Another recently described condition is pseudoplacentational endometrial hyperplasia (PEH), where the uterine lining remodels into a structure resembling normal placental sites. Whether preceded by CEH, PEH, or developing on its own, pyometra represents a profound failure of the uterus's natural defense mechanisms under hormonal influence.
The primary trigger for pyometra is the ascension of bacteria from the lower urinary tract or vagina into the uterus. During estrus, the cervix—the muscular gateway that seals the uterus off from the outside world—relaxes and opens to allow semen to enter. This open state also provides an opportunity for normal, resident bacteria from the vagina and surrounding skin to migrate upward.
Under normal circumstances, once estrus ends and the cervix closes, the healthy uterus is able to clear these transient bacteria through mild contractions and local immune defenses. However, during diestrus, the high levels of progesterone suppress the local immune response and inhibit uterine contractions. The accumulated fluid within the cystic uterine glands becomes stagnant, turning the uterus into an incubator.
A prominent veterinary internal medicine reference describes this process:
"Bacteria reach the uterus via ascension from the distal portion of the genitourinary tract, or less commonly by hematogenous spread. Failure to clear transient bacterial inhabitants from the uterus after estrus results in pyometra, a septic inflammatory condition of the uterus. E. coli is most commonly isolated from both bitches and queens with pyometra. Strong correlation exists between the onset" [2]
Escherichia coli (E. coli) is by far the most common bacterial culprit. E. coli is a normal inhabitant of the gastrointestinal tract and is readily present in the perineal area. Once inside the uterus, E. coli produces powerful endotoxins. When these toxins enter the bloodstream, they cause widespread systemic damage, including severe kidney dysfunction, systemic inflammatory response syndrome (SIRS), and potentially fatal septic shock.
Risk factors for developing pyometra include:
The clinical signs of pyometra can vary dramatically depending on whether the cervix is "open" or "closed." This distinction is critical, as it dictates how quickly the disease progresses and how easily it can be recognized by an owner.
Common symptoms to watch for include:
Occasional symptoms include:
In cats, the signs can be more subtle and easily missed until the disease is highly advanced. A leading critical care textbook notes:
"Clinical signs observed in queens with pyometra include vaginal discharge, anorexia, lethargy, weight loss, unkempt appearance, and polyuria and polydipsia. 18 A palpably enlarged uterus is a more common physical examination finding in cats than dogs, perhaps a result of the pliability of a cat's abdomen." [3]
Vaginal discharge is a classic sign of open-cervix pyometra, but may be absent in closed-cervix cases.
Diagnosing pyometra requires a swift and systematic approach. Your veterinarian will begin with a thorough physical examination and a detailed history, paying close attention to when your pet was last in heat. Pyometra typically manifests four to eight weeks after the end of the estrus cycle.
During the physical exam, the vet will carefully palpate your pet's abdomen. In many cases, especially in cats, an enlarged, tubular uterus can be felt. However, this must be done with extreme caution; aggressive palpation of a severely distended, thin-walled uterus can cause it to rupture inside the abdomen.
To confirm the diagnosis, your vet will recommend several key tests:
Ultrasonography is the gold standard for diagnosing pyometra, revealing fluid accumulation within the uterus.
Pyometra is a medical emergency. Left untreated, it is virtually always fatal. The primary goals of treatment are to stabilize the patient, eliminate the infection, and remove the source of systemic toxicity.
For the vast majority of cases, the treatment of choice is an emergency ovariohysterectomy (spaying). This surgery involves the complete removal of both the ovaries and the infected uterus.
Before your pet goes into surgery, your vet must stabilize her. This is a critical step, as anesthetizing a septic, dehydrated animal carries high risks. Stabilization involves:
As a leading veterinary internal medicine reference states:
"The treatment of choice for pyometra, following sta bilization of the patient with intravenous (IV) fluids and antibiotics, is ovariohysterectomy, an undesirable option for valuable breeding bitches or queens." [4]
Once stabilized, the pet is anesthetized, and the surgeon carefully removes the heavy, fragile uterus. Because the uterus is filled with highly infectious material, the surgeon must take extreme care to prevent any fluid from leaking into the abdominal cavity. Once the uterus is removed, the source of infection is gone, and most pets experience a rapid and dramatic recovery.
In highly specific circumstances, medical management may be considered. This option is strictly reserved for young, stable, valuable breeding females with an open-cervix pyometra, where preserving future fertility is of paramount importance. Medical management is not recommended for closed-cervix pyometra or for pets showing signs of systemic shock.
Medical management carries significant risks, including a high rate of treatment failure, potential uterine rupture, and a very high rate of recurrence in subsequent heat cycles.
The medical protocol typically involves:
Because of the high risk of recurrence, dogs or cats successfully treated medically should be bred on their very next heat cycle and spayed immediately once they are no longer intended for breeding.
The prognosis for pyometra depends heavily on how quickly the condition is diagnosed and treated, as well as the chosen treatment path.
Pyometra is a highly preventable disease.
Pyometra can progress from mild lethargy to life-threatening septic shock within hours. You must contact a veterinarian immediately if you observe any of the following emergency signs in an intact female dog or cat:
Do not wait to see if the symptoms improve. A closed-cervix pyometra can lead to uterine rupture and fatal peritonitis if left untreated.
While any intact female dog can develop pyometra, certain breeds show a higher predisposition to the condition. If you own one of these breeds and choose to keep them intact, you should be extra vigilant during the post-heat period:
If you are not planning to breed these dogs, early spaying is highly recommended to eliminate the risk of this common and dangerous disease.
Treatment must be prescribed by a licensed veterinarian based on your pet. Specific drug doses are intentionally not shown here.
Pyometra is a severe, life-threatening uterine infection affecting unspayed dogs and cats. Recognizing symptoms like vaginal discharge, increased thirst, and lethargy early is critical, as emergency surgery is often required to save the animal's life.
Anorexia、Fever、Lethargy、Polydipsia、Polyuria、Vaginal discharge、Vomiting、Dehydration
Ultrasonography、Abdominal radiography、Cytologic examination of vulvar discharge、Hematology (CBC)、Plasma progesterone concentration
Treatment must be prescribed by a licensed veterinarian based on your pet. Specific drug doses are intentionally not shown here.
This article is for general education and is not a substitute for professional veterinary advice. If your pet is unwell, please consult a veterinarian.
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