Hormonal Pyometra
Introduction
Hormonal pyometra is the uterine bacterial infection during dioestrus that occurs secondary to cystic endometrial hyperplasia.
Aetiology
The condition develops in the presence of progesterone - which stimulates endometrial growth and uterine secretion, suppresses myometrial activity and causes immunosuppression, producing an the ideal environment for bacterial overgrowth. Therefore pyometra is most likely to occur in the early luteal phase when progesterone levels are at their highest, or following administration of exogenous progesterone or oestrogen products (which increase the effects of progesterone) that delay oestrus or prevent conception. Pyometra also invariably occurs secondary to cystic endometrial hyperplasia as the hyperplastic tissue predisposes the uterus to bacterial overgrowth.
The causative organism is normally E. coli or Staphylococcus sp. but many bacteria may cause the infection. Infection is normally by ascending infection.
The are two types of pyometra - open and closed pyometra - referring to whether the cervix is open or closed.
Signalment
Pyometra is more commonly seen in older bitches who have never had offspring, one to two months after oestrus. It should not be ruled out as a differential diagnosis in neutered bitches because it can occur in the remnant ovarian tissue - this is known as stump pyometra. The condition is much rarer in the cat.
Clinical Signs
Clinical signs include:
- Polyuria and polydipsia
- Anorexia
- Panting
- Lethargy
- Vomiting
- Pyrexia
- Dehydration
- Abdominal distention - normally only in closed pyometra
- Odorous and purulent vaginal discharge - normally only in open pyometra
Peritonitis and shock may be seen following rupture of the uterus secondary to closed pyometra.
Clinical signs tend to be more severe in dogs with closed pyometra. This is because the condition may not be noticed as quickly by the owners due to the lack of outward signs and the uterus becomes distended and may rupture as the purulent material is unable to drain out of the uterus.
Diagnosis
Although history and clinical signs may be very suggestive of pyometra, definitive diagnosis is achieved by ultrasound. This should reveal a distended, fluid-filled uterus (signs will be less severe with open pyometra). Alternatively radiography can be performed - this should show a soft tissue opacity in the caudal abdomen, but it is hard to differentiate from pregnancy, pseudopregancy and other conditions affecting the uterus on the basis of these radiographic signs (so findings should be combined with the history and clinical signs).
Haematology and biochemistry normally show neutrophilia with a left shift, dehydration, mild normocytic, normochromic non-regenerative anaemia and sometimes azotaemia and hyperproteinaemia. Urinanalysis can show isosthenuria (caused by a reduced sensitivity to ADH or renal dysfunction), proteinurea (caused by membrano-proliferative glomerulonephritis) or evidence of a urinary tract infection. As well as providing information about the physiological status of the animal, these tests help rule out any other causes of the clinical signs.
Vaginal cytology can be performed if vaginal discharge is present.
Treatment
Curative treatment is ovariohysterectomy. The animal should be stabilised prior to surgery. The uterus may be very distended, congested and friable if the pyometra is closed. Therefore care should be taken not to rupture the uterus and it should be packed off with moist swabs to minimise contamination should spillage occur. Perioperative antibiotic treatment is recommended. If the uterus does rupture it is necessary to lavage the abdomen copiously, take a swab for culture and treat prophylactically with antibiotics post-operatively. Any animals with evidence of sepsis should also be treated with broad spectrum antibiotics postoperatively. There is a greater risk of haemorrhage in cases of pyometra when compared to standard ovariohysterectomy as the uterus is more vascular, therefore accurate haemostasis is necessary.
On the owners insistence, antibiotics and prostaglandins (PGF2) may be used to treat the condition medically. In some cases (particularly closed pyometra) the clinical signs are too severe to consider this option. There is always a risk of recurrence with medical treatment therefore it should not be encouraged.
Prognosis
Prognosis is better in open pyometra cases and in animals that present with less severe signs. However, following successful surgery to remove the uterus, prognosis is very good.
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References
Gilson, SD (1998) Self-Assessment Colour Review Small Animal Soft Tissue Surgery Manson
Information by permission of Professor RW Else
Merck & Co (2009) The Merck Veterinary Manual (Ninth Edition), Merial
Information by permission of Professor RW Else