Hyperoestrogenism - Dog

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Hyperoestrogenism is caused by excessive levels of oestrogen in the body and has different aetiologies depending on the sex of the animal.

In the bitch it is usually associated with cystic ovaries or more rarely a functional ovarian tumour. These are mostly granulosa-theca cell in origin and 10-20% are malignant. It can also occur iatrogenically through the administration of oestrogens used to treat mismating and urinary incontinence.

In the male dog the syndrome is associated with a Sertoli cell tumour of the testicles or a male feminising syndrome for which the cause in unknown.

Hyperoestrogenism is very rare in cats.

Clinical Signs


Bilaterally symmetrical alopecia and hyperpigmentation of the perianal, perigenial and axillary areas, enlargement of the nipples and vulva, comedones and pyoderma, oestrus cycle abnormalities such as nymphomania and pyometra.


Bilaterally symmetrical alopecia and hyperpigmentation, gynaecomastia, pendulous prepuce, testicular mass, prostatomegaly, attractiveness to other male dogs and loss of libido.


In all cases, history and clinical signs are suggestive.

Haematology and biochemistry of is usually unremarkable except where oestrogen-induced bone marrow suppression occurs, in which case a non-regenerative anaemia, thrombocytopenia and leucopenia are seen.

Other endocrine disorders which can cause the same skin changes should be ruled out, such as hypothyroidism and hyperadrenocorticism.

Blood oestrogens may be elevated in some dogs, however false positive and false negative results are common.

Definitive diagnosis for bitches is by exploratory laparotomy to investigate the ovaries.

In male dogs a mass may be palpated in the testicle.


Therapy for any concurrent infections together with supportive care if oestrogen-induced myelosuppression is present (fluids and whole blood transfusion) should be provided.

Ovariohysterectomy is the treatment of choice if an ovarian cyst or tumour is present.

Bilateral castration is the treatment of choice for testicular tumours. Any concurrent infections of the skin or prostate gland should be assessed.

Radiographs of the thorax are useful prior to surgery to check for any metastases in the case of neoplasia.


Most dogs show and improvement in clinical signs within 3-6 months.


Paterson, S. (2008) Manual of skin diseases of the dog and cat, John Wiley and Sons