Stump pyometra in a spayed female dog secondary to tamoxifen

OBJECTIVE: To describe a complication associated with the long‐term use of tamoxifen for the treatment of sclerosing encapsulating peritonitis in a dog. CASE SUMMARY: A 2‐year‐old female spayed poodle cross was evaluated for a stump pyometra. The dog was diagnosed with sclerosing encapsulating peritonitis a year prior and was treated with tamoxifen, an oestrogen receptor antagonist, for treatment of the disease. The dog developed a swollen vulva with vulvar discharge and a stump pyometra was diagnosed on ultrasound. Hormonal testing was submitted to evaluate for an ovarian remnant and the dog underwent an exploratory laparotomy, where the uterine stump was removed. No ovarian remnant tissue was identified intra‐operatively, and hormonal testing (anti‐Müllerian hormone, progesterone, oestradiol) and histopathology were consistent with the absence of ovarian tissue. The tamoxifen was discontinued. The dog recovered uneventfully after surgery. NEW OR UNIQUE INFORMATION PROVIDED: This report describes a complication of treatment of a rarely described clinical disease. While most cases of stump pyometra involve ovarian remnant syndrome, this case report describes a stump pyometra in a dog without remnant tissue that was undergoing treatment with tamoxifen. Tamoxifen has been reported to cause pyometra in intact female dogs. To the authors’ knowledge, this is the first case report to describe a stump pyometra in a spayed female dog, secondary to the use of tamoxifen.