Canine Pyometra and Metritis Study Guide

Overview and Clinical Importance

Pyometra and metritis are critical uterine infections in intact female dogs that represent veterinary emergencies requiring prompt recognition and treatment. Pyometra is defined as the accumulation of purulent material within the uterine lumen, typically occurring during or after diestrus in non-pregnant bitches. Metritis is acute inflammation and infection of the uterus occurring in the immediate postpartum period, usually within 1-2 weeks after whelping.

Both conditions can progress to life-threatening sepsis and multi-organ dysfunction if left untreated. Pyometra affects up to 25% of intact female dogs by 10 years of age, making it one of the most common reproductive disorders encountered in small animal practice and a high-yield topic for the NAVLE examination.

Pyometra

Definition and Epidemiology

Pyometra (literally meaning "pus in the uterus") is an infectious and inflammatory disorder of the uterus characterized by bacterial infection and accumulation of purulent exudate in the uterine lumen. It is the most prevalent reproductive disease in intact female dogs.

Key Epidemiological Data

Breed Predispositions

While pyometra can affect any intact female dog, certain breeds show increased prevalence:

Pathophysiology

The Cystic Endometrial Hyperplasia-Pyometra Complex

The development of pyometra is multifactorial, involving hormonal changes, bacterial infection, and pre-existing uterine pathology. The classical model involves:

• Estrogen Priming: During proestrus/estrus, estrogen increases endometrial progesterone receptor expression
• Progesterone Dominance: During diestrus, progesterone stimulates endometrial gland proliferation, decreases myometrial contractility, promotes cervical closure, and suppresses local immune responses
• Cystic Endometrial Hyperplasia (CEH): Repeated estrous cycles cause progressive endometrial changes including glandular cystic dilation
• Bacterial Colonization: Ascending infection from vaginal flora (primarily E. coli) colonizes the compromised uterus

Bacteriology

Escherichia coli is isolated in up to 90% of pyometra cases. These bacteria originate from normal fecal flora and ascend through the cervix. Key virulence factors include:

• Type P fimbriae (papC gene): Facilitates adherence to endometrial cells
• Cytotoxic necrotizing factor (CNF): Associated with enhanced inflammation
• Lipopolysaccharide (LPS): Endotoxin responsible for systemic illness and SIRS

Clinical Presentation

Open-Cervix vs. Closed-Cervix Pyometra

Common Clinical Signs

Diagnosis

Laboratory Findings

Diagnostic Imaging

Abdominal Ultrasonography is the preferred imaging modality:

• Distended uterine horns with anechoic to hyperechoic fluid content
• Thickened uterine wall (may be cystic with CEH)
• Can detect as little as 1 mL of intrauterine fluid
• Allows differentiation from pregnancy

Abdominal Radiography findings:

• Tubular, fluid-dense structure in caudal/mid abdomen
• Cranial displacement of intestines
• Gas within uterus (emphysematous pyometra - rare but serious)

Treatment

Surgical Treatment: Ovariohysterectomy

Ovariohysterectomy is the treatment of choice and is considered curative. Key considerations:

• Patient stabilization prior to surgery (IV fluids, antibiotics)
• Careful tissue handling to prevent uterine rupture
• Abdominal lavage if contamination occurs
• Post-operative monitoring for sepsis

Medical Treatment

Medical management may be considered for open-cervix pyometra in valuable breeding animals or when anesthesia is contraindicated:

Antibiotic Therapy

Metritis

Definition and Etiology

Metritis is acute inflammation and bacterial infection of the uterus occurring in the immediate postpartum period, typically within 1-14 days after whelping. Unlike pyometra, metritis is not associated with cystic endometrial hyperplasia.

Metritis vs. Pyometra: Key Differences

Risk Factors for Metritis

• Dystocia: Prolonged labor increases contamination risk
• Retained fetus/membranes: Substrate for bacterial growth
• Obstetric manipulation: Introduces bacteria
• Cesarean section: Increased infection risk

Clinical Presentation of Metritis

• Fever (often greater than 104°F/40°C)
• Foul-smelling vaginal discharge (fetid, dark, purulent)
• Depression and lethargy
• Neglect of puppies
• Decreased milk production

Treatment of Metritis

Memory Aid - "METRITIS": M-maternal neglect, E-exudate (fetid), T-temperature elevated, R-retained fetus, I-immediately postpartum, T-therapy = antibiotics, I-IV fluids, S-surgery if severe

Prognosis

Poor Prognostic Indicators

• Hypothermia (indicates severe sepsis)
• Leukopenia with degenerative left shift
• Severe azotemia
• Peritonitis (uterine rupture)
• Coagulopathy/DIC