Ovarian remnant syndrome
ORS is characterised by the presence of signs of heat and marked elevation in estrogen ('heat') hormone in the blood. Estradiol levels in ovariectomized cats are usually less than 10 pg/mL. In ORS, estradiol may rise to as high as 40 pg/mL.
ORS can be caused by incomplete removal of ovarian tissue during ovariohysterectomy due to surgical inexperience or the presence of an accessory ovary or of ovarian tissue that has extended into the ligament of the ovary or production of estrogen by the adrenal gland.
In most cases, ORS is due either to incomplete removal of ovarian tissue or the presence of accessory ovarian tissue, which can be small and has been reported to be located in the proper ligament of the ovary but separated by connective tissue from the normal ovary. If the normal ovary is removed, the accessory ovary may become functional. This is very different to ovarian remnant syndrome in the dog where ectopic ovaries have not been reported.
Diagnosis of ORS is based on a combination of clinical signs, history, vaginal cytology, hormonal assays and exploratory laparotomy.
Signs of ovarian remnant syndrome relate to oestrus behaviour in queens that have had an ovariohysterectomy. After establishing that a queen has been speyed (some cats present with a vague history of being neutered without documentation to assert such claims), the common cause of this syndrome is presence of ovarian tissue within the abdomen.
- Vaginal cytology - often helps confirm the presence of oestrus. In general, the use of vaginal cytology as a bioassay for feline oestrogen is more accurate than a single serum sample. Vaginal cytological changes in estrual queens tends to be more subtle than those of dogs but usually include an increase in cornified vaginal epithelial cells and clearing of normal background mucous. In speyed females, this supports the presence of an ovarian remnant, although a smear with normal anestrus characteristics (low cellularity and mainly small basal cells) does not rule out ORS.
- Hormonal assays - during oestrus, oestradiol levels rise sharply to more than 20 pg/mL before returning rapidly to basal concentrations in as few as 48 hrs. Thus blood sampling may be inaccurate if the timing of the sample does not coincide directly with the period of peak oestrus. A more specific test which has been reported is testing with HCG (Chorulon) and sampling progesterone levels. A dose of 25 μg gonadotropin releasing hormone (GnRH) (Chorulon) is injected intramuscularly. The GnRH causes ovulation of a follicle, an event highly correlated with a decrease in estradiol and an increase in progesterone. Five days later, progesterone and estradiol levels are assayed from blood tests. In cats with ORS, oestradiol levels drop and progesterone levels rise post-GnRh injection, confirming a diagnosis. In ovariectomised cats, GnRH causes little change in estradiol/progesterone levels.
- Laparotomy and surgical exploration of abdominal cavity for remnant ovarian tissue - in most cases, ovarian tissue is enlarged during oestrus, allowing easier visualisation of remnant tissue.
Differential diagnoses of ORS includes vaginitis, vaginal neoplasia, FLUTD, or catnip ingestion. Clinical signs of estrus in cats can sometimes be confused with urine spraying or overgrooming due to stress or territorial issues.
Surgical removal of the remnant ovarian tissue is the treatment method of choice, ideally when the cat is in estrus.
A practical alternative is the use of a suprelorin implant, which effectively suppresses estrus behavior for 1 - 2 years.
Other forms of medical treatment of ORS are not recommended generally. Progestogens, such as megestrol acetate have been used to suppress estrus in cats but can induce diabetes mellitus, severe mammary hyperplasia or neoplasia and adrenocortical atrophy. One suggestion is that administration of prednisolone (2.2 mg/kg PO 2 24 hr for 5 days, then tapered by halving the dose every 5 days) results in permanent cessation of oestrus within 3 to 5 days, presumably by suppression of the adrenal axis. If exploratory surgery is negative or it the owner declines surgical exploration, this is a viable treatment option.
If prednisolone is unsuccessful at suppressing oestrus behaviour, owners may elect to live with the behaviour or use antihistamine-based medications such as cyproheptadine (Periactin®) or dexchlorpheniramine (Polaramine®), whose sedative effects tend to mask over oestrus symptoms.
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- Dr Jim Euclid (2014), pers comm
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