Pyometra is an infection of the uterus in dogs and cats causing a variety of clinical and pathological signs related to genital and systemic disease. The uterus is generally filled with pus. Although the disease has been recognized for decades, the true pathogenesis has still not been completely understood. It is generally recognized that progesterone and estrogen and their receptors have a role in the development of pyometra; however, the infection is triggered by bacterial involvement. The cyclical hormonal influences of the female dog allow the uterus to go through changes that will be acceptable for fertilization of an embryo. The changes that the uterus undergoes are typical for each dog. If bacteria are introduced into the uterus at a certain time during the cycle, hormonal regulation of the uterus allows the infection to start and become fulminate.
There appears to be a correlation between pyometra and the administration of hormones such as estrogen and progesterone. In the presence of high concentrations of progesterone, as would be seen in a normal canine cycle or the administration of a mis-mating shot, with estrogen seems to have a correlation with pyometra in dogs older than 4 years of age. Administration of progesterones has not been shown to increase the risk of developing pyometra; however, we know that in the normal uterine environment, progesterone is potentially the hormone that sets the uterus up for infection if bacteria become involved.
If bacteria enter the uterus at the times when the protective physical barriers are breached, such as estrus, parturition, or immediately after parturition, the normal uterine defense mechanisms are likely to eliminate these bacteria. However, the hormonal influences may not allow the body to clear the bacteria. The bacteria typically cultured from the pyometra are bacteria that would be found in the areas of the intestines and vagina (E coli is the most common). Therefore, many of the infections are considered either from an ascending infection from the vagina, a concurrent urinary tract infection or fecal contamination. Certain bacteria are more virulent than others and therefore allow a bacterium that is normally found on the dog to develop into an infection.
Incidence and Prevalence
In Sweden, 25% of the intact female dogs will be present for canine pyometra before the age of 10 years. Pyometra is most commonly seen in intact dogs 4-8 weeks after estrus (mean time of 5.4 weeks); however, it can be seen 4 months post estrus as well. Although seen less commonly, cats generally develop pyometra between 1-4 weeks after estrous. Pyometra generally occurs in older (7 to 8 years) intact bitches and queens; however, it may occur in younger animals that have been given estrogen (mis-mating shots) or progestins for estrus suppression.
Signs and Symptoms
Because the infection can be so overwhelming, the reasons for presentation are not limited to the genital tract. The animal can become so overwhelmed by the inflammation associated with the infection that the animal may die from its own uncontrolled inflammatory process. The most common clinical signs that are present in >50% of dogs are:
- excessive water intake
- excessive urination
- pale mucous membranes
- Vomiting, diarrhea, weight loss, abdominal distension, and inflamed eyes have been reported although much less frequently
- Up to 16% of patients may have no clinical signs other than purulent vaginal discharge.
Many dogs and cats will have a closed cervix and therefore the obvious sign of a sanguinous (bloody) to mucopurulent, hemorrhagic vaginal discharge may not be present.
When to Seek Veterinary Surgical Advice
If your pet has recently had a heat cycle and displays any of the listed clinical signs, veterinary attention should be sought immediately. Most veterinarians are well equipped to diagnose a pyometra. However, many patients will need 24 hour intensive care after the procedure to help with the systemic disease. Find an ACVS Veterinary Surgeon.
Exam, Screening Tests and Imaging
Most of the time, your veterinarian will probably suspect the diagnosis based on your history and the animal’s physical exam. If the cervix is not open, the diagnosis may take a few more diagnostic tests. In general, a fluid distended uterus is needed to diagnose pyometra. The veterinarian will most likely perform a general chemistry profile, complete blood count, urinalysis, abdominal radiographs, abdominal ultrasound and perhaps vaginal cytology to help rule in or out pyometra. Radiographs are typically very suggestive but abdominal ultrasounds will typically identify the fluid filled uterus (Figure 1).
Figure 1. A markedly enlarged uterus as seen on a lateral radiograph
Pyometra should be ruled out in any intact female dog that is sick. Differential diagnoses for canine pyometritis are limited. Most clinical signs lead to genitourinary infection; however, if the cervix is closed other causes of the vague clinical signs of vomiting, diarrhea, excessive urination and drinking may need to be ruled out.
Complications Caused by the Disease
The most life threatening complications seen associated to pyometra are sepsis and systemic inflammatory response syndrome (SIRS) /multiple organ dysfunction syndrome (MODS). These generally develop as a result of the body’s overwhelming response to infection or inflammation, which pyometra has plenty of both. Other systems that may fail either in response to the SIRS/MODS or the results from pyometra would be the immune system, red and white blood cell production, kidneys, liver, and coagulation control. Up to 25% of the patients will show azotemia (elevations in the nitrogen waste products that the kidney will excrete) and 8% endotoxemia (severe sickness related to massive bacterial infection).
Closed cervix pyometra is a medical emergency that requires rapid intervention to prevent overwhelming sepsis and death. For most pets preoperative stabilization and resuscitation are first and foremost. After appropriate stabilization, ovariohysterectomy (spay) is the therapy of choice (Figures 2 & 3). The results of this therapy are rapid recovery with minimal risk of recurrence. Ovariohysterectomy also negates the risk of ovarian and uterine neoplasia and future unwanted pregnancy.
Figure 2. A markedly enlarged exposed uterus in a case of pyometra as seen at surgery. The uterine horns have been exposed and are filled with a purulent fluid.
Figure 3. The uterus seen in Figure 2 following surgical removal. The uterus has been opened to examine the inside of the organ.
Although surgery is considered the therapy of choice, very special case selection meeting certain criteria may allow valuable breeding bitches to be treated medically. However, in addition to the previously mentioned multiple organ problems, the dogs will generally exhibit abdominal pain, excessive vomiting/ defecation, high heart rates, salivation, dyspnea, panting and fever with the medical management. It generally takes 5 days or until an effect is seen to treat pyometra with low doses of prostaglandin F2 alpha (PGF2α). Dogs are susceptible to developing pyometra again after medical treatment; therefore, should have an ovariohysterectomy when their breeding purposes are finished..
Potential Complications Following Surgery
The SIRS/MODS and sepsis are still major problems after the surgery. However, once the inflamed/infected uterus is removed, the body generally recovers well over a couple of days. Very few patients will maintain kidney and white blood cell problems long term.
Once the pet is discharged from the hospital, the aftercare is minimal. The care is generally the same as it would be for a routine ovariohysterectomy; however, the dog and cat will be on antibiotics as prescribed by the veterinarian for at least 10 days. The animal should not be allowed have normal play, stairs, or any off leash activities since recent surgery has occurred and abdominal herniation is possible if not careful.
The prognosis with ovariohysterectomy can be as high as 80-100% if abdominal contamination is avoided and shock/sepsis is managed and responds appropriately perioperatively. However, if severe sepsis and organ failure develops, the prognosis can be grave. Some patients can remain PU/PD (increased urination and water intake) and a state of permanent kidney damage.
Most dogs and cats that are ovariohysterectomized early in life will not develop pyometra. However, a uterine stump pyometra may occur after incomplete ovariohysterectomy which allows a segment of the uterine body or horn to become infected. Typically, either a portion of the ovarian tissue is still present or the animal has been subjected to progestational compounds to allow this situation to develop. Clearly, hormone administration for mismating events and estrus suppression should be avoided except for the absolute necessities.
—Shawn Kennedy, DVM
Small Animal Resident
Editor: William Daly, DVM
Updated 8/15/2008 by Dr. Kennedy
Reviewed 10/1/2011 by Mitchell A. Robbins, DVM, Diplomate ACVS