Bitches with ORS may display signs of proestrus or estrus at regular or irregular intervals. Signs of heat may appear from several months and up to 10+ years.13 Estrus signs are often characterized by the normal sequence of physical changes typical of proestrus and estrus (eg, attractiveness to males and acceptance, vulvar swelling and discharge, cornified vaginal cytology), and breeding may be observed. Bitches with ORS may exhibit signs of false pregnancy several weeks to a few months following estrus behavior, and false pregnancy may be the only sign if estrus was silent.
Diagnosing ORS begins with confirmation of estrogen stimulation via a cornified vaginal smear in a spayed dog showing signs of heat and exclusion of exposure to exogenous estrogen. LH or anti-Müllerian hormone (AMH) testing may aid with diagnosis. A negative LH test or a positive AMH test is consistent with retained ovarian tissue. If these are nondiagnostic, further testing involves stimulation testing measuring estradiol and/or progesterone following gonadotropin administration. Lack of response to stimulation testing does not always rule out ORS because some remnants do not seem to respond in a typical fashion; in these cases, exploratory laparotomy may be necessary.
Serum progesterone should be assayed on a serum sample collected 1 to 2 weeks after the end of estrus. A serum progesterone concentration of >2.0 ng/mL (> 6.36 nmol/L) indicates presence of active luteal tissue. Laparotomy can be performed looking for a small piece of yellowish tissue at the level of the ovarian stump or the broad ligament. All tissues removed at surgery should be submitted for histopathology.