Chapter 211


Pyometra is a disease of the uterus, literally meaning pus in the uterus. Similar clinical entities include mucometra and hydrometra. Pyometra typically occurs in the estrogen-primed uterus during the period of progesterone dominance (diestrus) or thereafter (anestrus). It most commonly is diagnosed in an intact bitch from 4 weeks to 4 months after an estrous cycle. Pyometra is not as common in the queen as in the bitch because the queen is an induced ovulatory and thus does not experience repetitive estrogen and progesterone influences on the uterus. Many studies highlight an increased incidence of pyometra in nulliparous bitches and in bitches over 4 years of age. The queen has an increased incidence of pyometra with increasing age. In addition, African lions have been shown to have an increased risk of developing pyometra.

Pregnancy has a sparing effect on the uterus. In one study of multiple breeds, previous pregnancy had a protective effect on the incidence of pyometra in the rottweiler, collie, and Labrador retriever but was not protective for the golden retriever. Thus protective factors and risk factor may vary between breeds. There is no correlation between clinical signs of false pregnancy and pyometra in the bitch.


In one colony of beagles the incidence of pyometra was 15.2% of bitches older than 4 years of age, with the average age of onset 9.36 ± 0.35 years (Fukuda, 2001). In a population of insured dogs in Sweden in which routine ovariohysterectomy is disallowed, the crude 12-month incidence of pyometra over the 2-year period from 1995 through 1996 was approximately 2% in bitches under 10 years of age (Egenvall et al, 2001). A recent publication involving Swedish bitches lists the incidence of pyometra of bitches under 10 years of age at 25% (Hagman et al, 2011).

The pathogenesis of pyometra in the bitch involves estrogen stimulation followed by prolonged periods of progesterone dominance. Progesterone results in endometrial proliferation, glandular secretions, and decreased myometrial contractions. Leukocyte inhibition in the progesterone-primed uterus tends to support bacterial growth. These effects are cumulative with each estrous cycle, exacerbating the uterine pathology. Cystic endometrial hyperplasia (CEH) pyometra has four stages. Stage one is uncomplicated CEH. Stage two is CEH with endometrial infiltration of plasma cells. Stage three is CEH with acute endometritis. Finally, Stage four is CEH with chronic endometritis.

Estrogen therapy is associated with an increased risk of pyometra in bitches from 1 to 4 years of age. Use of estrogens (estradiol cypionate) for mismating in diestrous bitches is particularly dangerous and has resulted in approximately a 25% occurrence rate of pyometra. Furthermore, use of estrogens in the bitch has a potential for idiosyncratic, non–dose-related bone marrow suppression. The one (and only) time this author used estradiol cypionate for mismating in an 18-month-old golden retriever resulted in an open cervix pyometra. In queens, the administration of medroxyprogesterone acetate for estrus suppression increases the risk for development of pyometra.

Risk for pyometra is increased in several breeds, including the golden retriever, miniature schnauzer, Irish terrier, Saint Bernard, Airedale terrier, cavalier King Charles spaniel, rough collie, rottweiler, and Bernese mountain dog.

Clinical Findings

The medical history of a female dog with pyometra can be nonspecific. The queen may have nonspecific illness and a vaginal discharge. In older bitches the client may not recognize an estrous cycle and assume that the bitch has experienced “menopause.” The client also may mistake a serosanguineous vaginal discharge associated with pyometra with that of a normal estrus. Vaginal cytology helps to differentiate the prevailing hormonal events at the time of initial examination. Clinical history of bitches and queens with pyometra often includes depression, inappetence, polydipsia, polyuria, lethargy, and abdominal enlargement with or without vaginal discharge. Pyometra always should be in the differential diagnosis of a sick, intact bitch or queen.

Bitches and queens with pyometra typically are afebrile. An elevated white blood count is typical, and hyperproteinemia and hyperglobulinemia also are common. An acute phase protein α-1-acid glycoprotein is elevated in the bitch with pyometra; however, this test is not readily available in clinical practice. Prerenal azotemia accompanies dehydration, but urine-concentrating ability may be impaired. Bitches with pyometra that have urine protein creatinine ratio (UPC) greater than 1.0 or high ratios of urinary biomarkers may have clinically significant renal lesions and should receive follow-up monitoring of renal function after the resolution of the pyometra. Cystocentesis is associated with the risk of perforation of the fluid-filled uterus and possible spillage of uterine contents into the abdomen. The most common organism isolated from the uterus or vaginal discharge of a bitch with pyometra is Escherichia coli. Culture and sensitivity of the vaginal discharge or of intrauterine fluid at the time of ovariohysterectomy should be performed to guide antibiotic therapy.

The vaginal discharge in the CEH/pyometra complex may be purulent, sanguinopurulent (the color and consistency of tomato soup), mucoid, or frankly hemorrhagic. Vaginal discharge of any description should alert the clinician to include pyometra in the differential diagnosis. Other causes of vaginal discharge include vaginitis, estrus, immune-mediated thrombocytopenia (bloody discharge), anticoagulant toxicity, metritis, and subinvolution of placental sites.

Diagnosis is accomplished best with ultrasonography and/or radiography. The classic radiographic finding is a fluid-filled, tubular organ between the descending colon and the bladder that presents a sausage-like appearance. The uterus is visualized best with a lateral abdominal radiograph. A fluid-filled organ can be identified ultrasonographically, and the uterine wall thickness and proliferative changes also can be noted.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Pyometra

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