Introduction
Pyometra is a life-threatening bacterial infection of the uterus, predominantly affecting intact female dogs (and less commonly, cats), characterized by pus accumulation within the uterine lumen. It typically occurs during diestrus when high progesterone levels render the uterus susceptible to bacterial growth.
1. Etiology and Pathophysiology
Hormonal Underpinnings
Progesterone: After ovulation, progesterone secreted by the corpus luteum leads to:
Decreased myometrial contractility → hinders bacterial clearance.
Glandular hyperplasia and secretion → creates a nutrient-rich environment.
Suppression of local uterine immune defenses.
Estrogen Priming: In some cases, elevated estrogen levels before or concurrent with progesterone can exacerbate endometrial changes. Exogenous estrogen administration (e.g., mismating injections) also increases risk.
Cystic Endometrial Hyperplasia (CEH)
Over multiple estrous cycles without pregnancy, repeated progesterone surges induce progressive changes in the endometrium, termed CEH.
CEH provides an ideal milieu for bacterial implantation and proliferation, leading to pyometra when ascending bacteria overwhelm local defenses.
Bacterial Ascension and Infection
Main Pathogen: Escherichia coli (commonly uropathogenic strains) ascending from the lower reproductive tract.
Additional bacterial species may include Staphylococcus, Streptococcus, and Pseudomonas spp.
E. coli virulence factors (e.g., P-fimbriae) facilitate adherence to endometrial epithelium, intensifying infection severity.
Pathophysiologic Classification
Open-Cervix Pyometra: Cervix remains partially or fully patent, allowing purulent exudate to drain externally. Clinical course may be less acute due to decompression.
Closed-Cervix Pyometra: Cervical closure impedes drainage; intrauterine pressure escalates, heightening the risk of uterine rupture and severe peritonitis.
2. Clinical Manifestations
General Clinical Signs
Lethargy, depression, and anorexia due to systemic toxemia.
Polyuria and polydipsia (PU/PD), often reflecting renal tubular damage caused by circulating endotoxins.
Gastrointestinal signs (vomiting, diarrhea) in severe or advanced cases.
Possible fever; however, some animals may be normothermic or even hypothermic in septic shock.
Specific to Pyometra Type
Open Pyometra: Purulent or hemorrhagic vulvar discharge, mild abdominal distension, generally more chronic progression.
Closed Pyometra: Marked abdominal distension, acute onset of systemic signs (shock, dehydration, tachycardia), higher risk of uterine rupture.
3. Diagnostic Approach
Physical Examination
Palpable enlarged uterus (careful palpation to avoid rupture).
Signs of dehydration (prolonged skin tent, dry mucous membranes) and possible fever or hypothermia.
Tachycardia, especially if septicemia is present.
Laboratory Investigations
Complete Blood Count (CBC):
Leukocytosis with neutrophilia and a left shift in most cases.
Possible leukopenia if overwhelmed by sepsis.
Serum Biochemistry:
Elevated BUN and creatinine (prerenal azotemia due to dehydration and/or endotoxin-induced kidney injury).
Elevated liver enzymes (ALT, ALP) secondary to systemic inflammation or hypoperfusion.
Electrolyte disturbances (hyponatremia, hyperkalemia) in severe sepsis.
Urinalysis:
Low specific gravity due to endotoxin-mediated nephropathy.
Proteinuria and active sediment possible if septicemia affects renal function.
Imaging
Radiography:
Visualization of an enlarged uterine silhouette displacing abdominal organs.
Less sensitive in early cases or with minimal fluid accumulation.
Ultrasound:
Gold standard for evaluating uterine content and wall thickness.
Differentiates between CEH and frank pyometra (fluid echo-patterns, septations, cystic changes).
Assesses for free fluid in the abdomen (suspected rupture).
Additional Diagnostics
Vaginal Cytology: May confirm presence of neutrophils and bacteria in open pyometra, though ultrasound is more definitive.
Culture and Sensitivity: Ideally performed on uterine contents or vaginal discharge. In practice, empirical antibiotic therapy often precedes culture results if the patient is hemodynamically unstable.
4. Treatment and Management
A. Surgical Intervention (Ovariohysterectomy - OHE)
Indications
Definitive treatment: Recommended for most pyometra cases, especially closed-cervix, hemodynamic instability, or severely compromised uterine integrity.
Eliminates the source of infection and prevents recurrence.
Surgical Considerations
Preoperative Stabilization:
Intravenous fluid therapy (balanced crystalloids) to correct hypovolemia and electrolyte imbalances.
Broad-spectrum antibiotics (e.g., IV cephalosporin or fluoroquinolone with gram-positive coverage).
Analgesia (opioids preferred initially due to renal considerations with NSAIDs).
Surgical Technique:
Standard midline laparotomy.
Handle the uterus with extreme care to prevent rupture. Use laparotomy sponges to isolate the infected organ.
Double or triple clamp the uterine body and ovarian pedicles. Ligate securely (absorbable suture like PDS or a similar monofilament).
Copious lavage of the surgical site and use of fresh instruments for closure to minimize contamination risk.
Postoperative Care:
Continue IV fluids to ensure renal perfusion and help clear endotoxins.
Antibiotics for a minimum of 7–14 days; extend if lab findings or clinical signs indicate ongoing infection.
Monitor for signs of SIRS (Systemic Inflammatory Response Syndrome) or persistent infection.
Prognosis
With prompt OHE, prognosis is generally excellent.
Mortality increases if sepsis, septic shock, or uterine rupture has occurred before or during surgery.
B. Medical Management (Conservative Treatment)
Indications
Intended for valuable breeding animals when preserving reproductive capability is essential.
Typically appropriate only in open-cervix pyometra with stable hemodynamic status.
Requires vigilant monitoring due to high relapse rates (~77% recurrence within a year).
Protocol
Prostaglandin F2α (PGF2α):
Promotes myometrial contractions and cervical relaxation, facilitating evacuation of uterine exudate.
Contraindicated in closed-cervix pyometra because of the risk of rupture from increased intrauterine pressure.
Side effects: Vomiting, abdominal cramping, panting, restlessness (often mitigated by dividing total dose into multiple smaller doses throughout the day).
Antibiotic Therapy:
Start with broad-spectrum coverage against E. coli and gram-positive aerobes:
Amoxicillin-clavulanate or a 2nd/3rd generation cephalosporin (e.g., cefovecin, cefpodoxime).
Fluoroquinolones (e.g., enrofloxacin) can be considered where resistant gram-negative organisms are suspected.
Adjust regimen based on culture & sensitivity if possible.
Supportive Care:
IV fluids to correct dehydration.
Close monitoring of renal parameters and hematologic markers.
Pain management: Opioids or cautious NSAID use if renal parameters are stable.
Outcome and Follow-Up
Serial ultrasound examinations to ensure uterine involution and resolution of infection.
Repeat CBC/chemistry to monitor for persistent or recrudescent infection.
High probability of recurrence with subsequent estrous cycles; OHE strongly recommended once breeding goals are met.
C. Management of Septic Shock
Aggressive Fluid Resuscitation: IV crystalloids (and colloids if indicated).
Vasopressor Support: Dopamine, norepinephrine for refractory hypotension.
Rapid Antibiotic Administration: Broad-spectrum coverage given IV immediately.
Monitoring:
Continuous ECG, blood pressure, central venous pressure (CVP) if possible.
Serial lactate measurements to gauge perfusion and response to therapy.
Urine output to assess renal function.
Timing of Surgery: Once partially stabilized (unless uterine rupture is strongly suspected, in which case immediate surgery is critical).
5. Prognosis
Surgical Management:
Early intervention with OHE provides a high survival rate (90%+ in stable patients).
Delays in treatment, concurrent diseases (renal failure, advanced hepatic dysfunction), or sepsis drastically worsen prognosis.
Medical Management:
Acceptable for mild, open-cervix cases in breeding stock, but relapse rates are high.
Strict follow-up is essential, and many animals eventually require surgical intervention.
6. Prevention
Routine Ovariohysterectomy (Spaying):
Spaying before the first estrus nearly eliminates pyometra risk.
Advisable in non-breeding animals.
Avoid Unnecessary Hormonal Therapies:
Eschew exogenous progesterone or estrogen unless absolutely indicated.
Breeding Management:
Use only healthy, infection-free breeding stock.
Monitor intact females closely during and after estrus.
Prompt veterinary attention for any abnormal discharge or systemic signs of illness.
Summary Table: Pyometra at a Glance
Category | Key Points |
Cause | Primarily E. coli infection under progesterone influence (CEH). |
Risk Factors | Intact females (>6 years), repeated estrus without pregnancy, hormonal drugs. |
Clinical Signs | Lethargy, PU/PD, anorexia, abdominal distension, purulent discharge (open cervix). |
Diagnosis | Leukocytosis, azotemia, imaging (ultrasound > radiography). |
Treatment | Surgical (OHE) is definitive; Medical (PGF2α + antibiotics) for select open cases. |
Prognosis | Good if treated early. Poor if septic shock, rupture, or organ failure ensues. |
Prevention | Routine spaying and avoidance of unnecessary hormonal manipulation. |
Key Takeaways for Practitioners
Pyometra is a surgical emergency in most cases.
Closed-cervix pyometra is more likely to present in acute, critical condition with a higher risk of uterine rupture.
Ovariohysterectomy remains the gold standard treatment.
Medical management is a second-line option and poses significant risks, including recurrence.
Early detection is crucial; proactive diagnostic imaging in intact females showing systemic illness often saves lives.
Additional Notes on Antibiotic Regimens
Empirical Coverage
Start broad-spectrum to cover common flora: Gram-negatives (especially E. coli) and Gram-positives.
Examples:
Amoxicillin-Clavulanate (oral or IV)
Cefazolin (IV), followed by Cephalexin or Cefovecin
Enrofloxacin or Marbofloxacin when resistant Gram-negatives are suspected
Duration
A minimum of 2 weeks, guided by clinical response and CBC/chemistry results.
In complicated or septic cases, 4–6 weeks may be required.
Culture & Sensitivity
Ideally performed on uterine contents.
Guides antibiotic choice, especially in recurrent or resistant infections.
Surgical Pearls
Gentle Tissue Handling: The uterus can be friable; use appropriate instruments and moistened laparotomy sponges.
Double-Ligation: Secure ligation of both ovarian pedicles and the uterine body is critical for preventing stump leakage.
Prevent Spillage: Consider placing the uterus in a sterile bag if the rupture risk is high and excise in a controlled manner.
Copious Irrigation: Decreases the bacterial load in the surgical site; isolate contaminated instruments and gloves.
Comments