In order to understand pyometra in cats, it is first necessary to understand the underlying condition, called cystic endometrial hyperplasia (CEH). CEH tends to be a chronic subclinical condition and may be hard to diagnose definitively without biopsy of the uterus. Uterine pathology, mostly secondary to CEH and endometritis, is common in queens over 5 years of age. CEH is very common in unbred queens over 3 years of age.

It has typically been believed that because cats are induced ovulators, the incidence of CEH/pyometra is lower than in dogs. However, recent studies have shown a great many cats are also spontaneous ovulators, and therefore may experience prolonged diestral periods without pregnancy. The diestral phase of the estrous cycle in cats is the period when the uterus is under the influence of progesterone. This commonly happens in pregnancy, but also in pseudopregnancy (false pregnancy).

Repeated pseudopregnancies may predispose the uterus to CEH, which is a disorder of proliferative and degenerative changes in the endometrium (the lining of the uterus) associated with aging. Progesterone causes hyperplasia (increase in size and thickness) of the endometrium and endometrial glands. Other effects of progesterone include inhibition of local responses to infection in the uterus and decreased contractility. The total effect is to produce an environment in the uterus that is favourable for bacterial growth.

Most queens with pyometra were in heat some time in the preceding 60 days. Estradiol, a hormone produced during heat or estrus, causes an increase in the number of estrogen and progesterone receptors in the endometrium. It also causes cervical dilation during estrus and therefore allows bacteria that are part of the normal flora of the vagina (especially E. coli and Streptococcus spp) to ascend into the uterus. It is normal for cats to have both aerobic and anaerobic bacteria in the vagina. Younger cats have more vaginal bacteria than older cats, and cats in heat or pregnant have more bacteria than anestrus cats. Vaginal cultures are therefore hard to interpret since the queen has normal bacterial flora. This combination of ascending bacteria and an abnormal endometrium can predispose queens to pyometra.

Symptoms and Diagnosis

Cats who have CEH but not pyometra may be normal on physical examination. Their blood and urine tests are normal. One possible symptom in some queens is unexplained infertility with a normal estrous cycle. Ultrasound of the abdomen is very sensitive for detecting uterine enlargement. X-rays are not as useful, but being able to see the uterus on an x-ray usually indicates the uterus is enlarged. The final diagnosis is often not made until exploratory surgery is performed and the uterus is removed and/or biopsied.

Cats with advanced CEH are occasionally found with mucometra or hydrometra, characterized by variable amounts of mucus in the uterus. In hydrometra, the mucin is thin and watery. In mucometra, the mucin is thick or even semisolid. Queens with either condition do not have bacterial infections and are not systemically ill. The main symptom is a swollen abdomen, with or without a vaginal discharge.

The clinical signs of pyometra include a vulvar discharge, depression, dehydration, anorexia, fever, weight loss and a distended abdomen. Any abnormal vulvar discharge in an intact queen should be assumed to be due to pyometra. However, 15-30% of queens have no vulvar discharge (due to a closed cervix).

Queens are often very meticulous in grooming, however, so evidence of the discharge may be hard to find. Most queens with pyometra will have an increased white blood cell count. The diagnosis can be affirmed by finding an enlarged uterus on x-rays or ultrasound. In some cases, the uterine enlargement is segmental, mimicking a pregnancy. Occasionally, only one horn of the uterus is involved.

Treatment

Initial treatment for pyometra may involve intravenous fluids and antibiotics. Since E. coli is the most common bacterium involved, good antibiotic choices are enrofloxacin (Baytril®), trimethoprim-sulfa (Tribrissen®), or amoxicillin/clavulanic acid (Clavamox®). It is not usually necessary to perform a culture and sensitivity test on the uterine discharge. Antibiotic therapy alone for pyometra is not often successful. Douches using antiseptic or antibiotic solutions are also not effective. The overall mortality rate in queens with pyometra, according to a 1987 study, is about 8%, and is most commonly associated with a ruptured uterus and bacterial peritonitis.

Two approaches to treatment of pyometra may be taken: ovariohysterectomy (spay) and prostaglandin therapy. 1) Ovariohysterectomy provides the most consistent results as the source of the problem is permanently removed and cats recover quickly. For queens who are not valuable to a breeding program, or who have closed-cervix pyometra, this is probably the best choice.

2) Prostaglandin (PG) therapy has been the most successful treatment for open-cervix pyometra where it is desirable to preserve the future fertility of the queen. The best queens for this therapy are under 6 years of age, in good health, and have no retained fetal material if they are post-partum (ultrasound is very helpful in determining this). PG therapy is contraindicated in queens with some medical conditions such as asthma. PG therapy should not be used if the queen is in poor condition or is critically ill. Careful assessment of the patient is esential for ruling out conditions that could preclude the use of PG. For example, in rare cases, pyometra is associated with uterine torsion, a contraindication for PG treatment. Treatment of closed cervix pyometra should only be undertaken with caution, and only in medically stable, young and otherwise healthy queens. If the cervix does not open after a few days of therapy, or if the queen becomes ill, she should be spayed.

Only natural prostaglandin is used since synthetic PG are considerably more potent and safe doses have not been determined for the cat. Queens are treated with 0.1 mg/kg of PGF2® (Lutalyse®) subcutaneously, once or twice daily for 5 days. The main purpose of the PG is to cause the uterus to contract and expel its contents. Queens need to be watched closely during PG therapy and may be hospitalized for the part of each day which follows administration of the drug. Queens must be monitored for rising fevers, abdominal pain, or other symptoms of systemic illness or rupture of the uterus. Monitoring with x-rays or ultrasound may be needed in addition to blood counts. The rate of complications with this treatment is very low.

Side effects are noted often, usually within minutes of the injection, and will be worse in the first 2 days. The contractile effects of PG on the smooth muscles of the myometrium (muscular layer of the uterus), GI tract, respiratory tract, and bladder account for these reactions. Common side effects include restlessness, vocalizing, panting, vomiting, diarrhea, salivation, and intense grooming of the flanks and vulva. These effects usually last only a few minutes, rarely lasting longer than 15-20 minutes. The reactions become less obvious with each treatment. Usually by the fifth day, little or no side effects are seen. Antibiotics should be given throughout the course of PG therapy and for some time afterward.

Follow Up

Queens should be followed up by the veterinarian one and two weeks following PG treatment. The vaginal discharge should change to a clear fluid by the seventh day following treatment. This clear discharge may last for up to 10 days. Most cats are back to normal 2 weeks after treatment. If a purulent or bloody discharge is persistent, a second course of treatment may be necessary. Most queens will come back into heat within several weeks and they should be bred at the first opportunity. It may be valuable to treat the queen with antibiotics during this heat and into the first 4 weeks of any resulting pregnancy. An antibiotic safe for use in pregnancy, such as amoxicillin/clavulanic acid (Clavamox ®), should be chosen.

After treatment with PG, pregnancy rates of 71-86% have been reported. One 1992 report found recurrence of pyometra within 1 year in 14% of treated cats. Repeat treatment of recurrent pyometra can be successful, however. Some cats (4%) will have subclinical generalized bacterial peritonitis associated with pyometra that may contribute to ongoing problems with ill health and eventually necessitate ovariohysterectomy. There are no reports of successful treatment of closed pyometra in the cat although in the dog the success rate is reported to be 34%.

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References

Clemetson LL, Ward ACS. Bacterial flora of the vagina and uterus of healthy cats. J Amer Vet Med Assoc 196(6): 902-906, 1990
Davidson AP, Feldman EC, Nelson RW. Treatment of pyometra in cats, using prostaglandin F2alpha: 21 cases (1982-1990). J Amer Vet Med Assoc 200(6):825-828, 1992
Kenney KJ, Matthiesen DT, et al. Pyometra in cats: 183 cases (1979-1984). J Amer Vet Med Assoc 191(9):1130-1132, 1987
Lawler DF, Evans RH, et al. Histopathologic features, environmental factors, and serum estrogen, progesterone, and prolactin values associated with ovarian phase and inflammatory uterine disease in cats. Am J Vet Res 52(10): 1747-1753, 1991
Macintire DK. Emergencies of the female reproductive tract. Vet Clin North Amer Sm Anim Pract 24(6): 1173-1188, 1994
Potter K, Hancock DH, Gallina AM. Clinical and pathologic features of endometrial hyperplasia, pyometra, and endometritis in cats: 79 cases (1980-1985). J Amer Vet Med Assoc 198(8):1427-1431, 1991
Tsutsui T, Stabenfeldt GH. Biology of ovarian cycles, pregnancy and pseuodpregnancy in the domestic cat. J Reprod Fert Suppl 47:29-35, 1993

Photos Credits

Susan Little DVM Photo (a),(b),(c),(d),(e),(f),(g)
Ruth Podd Photo (h)

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