Contributors: Prof Gary England, Rob Lofstedt

 Species: Feline   |   Classification: Diseases

Introduction Pathogenesis Diagnosis Treatment Outcomes Further Reading


  • Disease of the luteal phase.
  • Hormonally mediated cystic hyperplastic endometritis associated with a bacterial infection.

Presenting Signs

  • Polyuria/polydipsia.
  • Vaginal discharge.
  • Anorexia.
  • Depression.
  • Vomiting Vomiting.
  • Pyrexia.
  • Abdominal distension.

Acute Presentation

  • Depression.
  • Lethargy.
  • Anorexia.
  • Vomiting.
  • Diarrhea.
  • Polyuria/polydipsia.

Age Predisposition

  • Middle to old age.



  • Secondary bacterial infection of the material in the endometrial glands (embryotroph) may include Escherichia coli  Escherichia coliProteus spp, B-hemolytic streptococci  Streptococcus spp and occasionally anaerobes.

Predisposing Factors


  • Middle to old age.
  • Successive luteal phases without pregnancy.


  • Prolonged use of progestagens for the prevention or suppression of estrus.


  • Successive luteal phases without pregnancy, ie following non-fertile mating-induced ovulation or occasionally spontaneous ovulation (pseudopregnancy Pseudopregnancy), or progestagen use   →   repeated and prolonged progesterone concentrations   →   cystic endometrial hyperplasia   →   pyometra.
  • Renal disease: several aspects of the renal changes associated with pyometra are incompletely understood but some suggestions include:

Prerenal uremia

  • Dehydration, shock and toxemia   →   poor renal perfusion   →   Antibody / Antigen (Ab-Ag) complexes deposited on the basement membrane of the glomerular apparatus   →   glomerular disease   →   persistent proteinuria.
  • Bacterial toxins or immune complexes interfere with Na+ resorption from the distal convoluted tubule and collection ducts   →   tubular disease   →   impaired ability to concentrate urine   →   polyuria   →   dehydration and electrolyte loss.
  • Concurrent renal disease may be found in older cats.

Acid base balance

  • Metabolic acidosis is more common but metabolic alkalosis may develop through prolonged vomiting.


  • Vomiting, uterine loss and renal dysfunction   →   Na+/K loss.

White cells


Presenting Problems

  • Polyuria/polydipsia.
  • Vomiting Vomiting.
  • Anorexia.
  • Vaginal discharge.
  • Depression.
  • Abdominal distension.

Client History

  • Middle-aged to old queen.
  • Polyuria/polydipsia.
  • Vaginal discharge.
  • Last estrus >3 weeks previously (ie animal has ovulated and progesterone is high).
  • Vomiting.
  • Anorexia.

Clinical Signs

  • Large numbers of neutrophils in the vaginal cytology Cytology: vaginal cytology from a queen in estrus  Cytology: vaginal cytology from diestrus queen .
  • Vaginal discharge.
  • Polyuria/polydipsia.
  • Vomiting.
  • Anorexia.
  • Abdominal enlargement.
    Palpation of the distended uterus may be possible.

Diagnostic Investigation


  • High numbers of neutrophils Cytology: vaginal cytology from a queen in estrus   Cytology: vaginal cytology from diestrus queen .


2-D Ultrasonography

  • See ultrasonography of the uterus Ultrasonography: uterus.
  • Highly effective diagnostic modality.
  • Identify fluid-filled loops where the fluid is normally anechoic but may contain echogenic particles.


  • See Radiography: abdomen Radiography: abdomen.
  • Plain lateral radiographs of the posterior abdomen  Uterus: pyometra - radiograph lateral  Uterus: pyometra - radiograph VD . (Attempt to identify the coiled viscus of the fluid-filled uterus.)
    Contrast radiography is rarely necessary.




Gross Autopsy Findings

  • Pyometra Uterus: pyometra - gross specimen .

Differential Diagnosis

Uterine enlargement


Uterine enlargement

  • Uterine tumors.

Vaginal discharge


Initial Symptomatic Treatment

Supportive therapy

Standard Treatment


  • Ovariohysterectomy Ovariohysterectomy .
    Dehydration and electrolyte and acid/base imbalances should be corrected preoperatively.

Medical management

  • Salvage of the reproductive capacity of the queen may be possible by promoting uterine contractions and expelling the pus.
  • Usually requested by the owner of a valuable breeding queen.
  • Medical management should only be attempted if:
    • Open pyometra. Cytology should be done in all cases.
    • Where no signs of systemic illness exist.
    • Where owners understand the risks of failure and the need for rapid ovariohysterectomy if treatment is unsuccessful.
    • With appropriate antibiotic therapy.


  • Dose rate: 250 ug/kg q12h SC for 4 days, ie 0.25 mg/kg. New data suggest doses of 25 ug/kg q8h, ie 1/10 of older doses, equally effective.
  • Prostaglandins cause luteolysis and rapid uterine contractions but seldom expulsion of the pus.
    Side-effects of vomiting and diarrhea usually decrease after second/third dose.Reports of the success rate are variable but some queens may be salvaged.Prostaglandins can be absorbed through the skin. May cause bronchospasm or miscarriage. Women of child-bearing age, asthmatics and people with respiratory problems should wear gloves or avoid contact with the product. Wash accidental spillage off skin immediately with soap and water.

Progesterone receptor antagonists

  • These agents, eg Aglepristone Aglepristone, have been shown to be useful for the treatment of pyometra in bitches. They may find clinical acceptability in the queen but as yet they are not widely available.


  • Prostaglandins should be continued until the neutrophil count is normal, the vaginal cytology is normal and the pyometra is no longer visible on ultrasound.


Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Tobias K M & Wheaton L G (1995) Surgical management of pyometra in dogs and cats. Semin Vet Med Surg (Small Anim) 10 (1), 30-34 PubMed.
  • Davidson A P, Feldman E C, Nelson R W (1992) Treatment of pyometra in cats, using prostaglandin F2 alpha - 21 cases (1982-1990). JAVMA 200 (6), 825-828 PubMed.
  • Potter K, Hancock D H, Gallina A M (1991) Clinical and pathologic features of endometrial hyperplasia, pyometra, and endometritis in cats - 79 cases (1980-1985). JAVMA 198 (8), 1427-1431 PubMed.
  • Marretta S M, Matthiesen D T, Nichols R (1989) Pyometra and its complications. Probl Vet Med (1), 50-62 PubMed.
  • Schulman J & Levine S H (1989) Pyometra involving uterus masculinus in a cat. JAVMA 194 (5), 690-691 PubMed.
  • Kenney K J, Matthiesen D T, Brown N O et al (1987) Pyometra in cats - 183 cases (1979-1984). JAVMA 191 (9), 1130-1132 PubMed.
  • Arnbjerg J & Flagstad A (1985) Prostglandin F2 alpha treatment of feline open pyometra. Nord Vet Med 37 (5), 286-290 PubMed.
  • Gillespie D & Kock N (1983) Pyometra in a Pallas's cat. JAVMA 183 (11), 1322-1323 PubMed.
  • Wiessing J & Thomson K S (1980) Treatment of feline pyometra with dinoprost. N Z Vet J 28 (6), 112 PubMed.

Other sources of information

  • Chandler E A, Gaskell C J & Gaskell R M (1994) Feline Medicine and Therapeutics. 2nd edn. Oxford: Blackwell Scientific Publications, pp 272-273. ISBN 0 632 03361 4.
  • Christiansen I J (1984) Reproduction in the Dog and Cat. London: Bailliere Tindall, pp 243-245. ISBN 0 7020 0918 0.

Other Sources of Information