Ferret endocrine conditions (Proceedings)
Adrenal Gland Disease
Hyperadrenocorticism is a common and complex clinical condition in the pet ferret. This disease occurs most frequently in ferrets three years or older but has been reported in animals as young as one year. There is no obvious gender predisposition. The most common clinical sign of hyperadrenocorticism in ferrets is progressive alopecia of the tail, tail base and trunk, continuing until the affected ferret is partially or completely bald. Either gender can exhibit pruritis. Some ferrets exhibit a return to sexual behavior or emit a musky odor that is stronger than normal. Vulvar enlargement may be seen in spayed females. Male ferrets may present with a history of stranguria or urinary tract obstruction due to metaplastic, hyperplastic, or cystic prostatic tissue. Rarely, either gender can exhibit hyperpigmentation of the skin or anemia due to bone marrow toxicity from the associated hyperestrogenemia.
The hypothetical etiology of this disease involves early neutering and long light cycles to which pet ferrets are exposed in the United States. These factors may trigger a "perpetual breeding season" syndrome. Early neutering may remove negative feedback from the adrenal glands, which have the capacity to produce androgenic hormones. Long photoperiods may stimulate the production of gonadotropin-releasing hormone (Gn-RH) by the hypothalamus, which stimulates pituitary gland secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH). With lack of an LH surgery to decrease the production of gonadotropic hormones, subsequent constant stimulation of the adrenal gland may progress to the development of adrenal hyperplasia or neoplasia (adenoma or adenocarcinoma).Presumptive diagnosis of adrenal disease in the ferret is based on history, clinical signs, imaging diagnostics, and/or steroid hormone assay. Surgical biopsy of the affected adrenal gland provides a definitive diagnosis. Adrenal enlargement can involve one or both glands. Experiences ultrasonographers can often detect adrenomegaly or abnormal adrenal structure. The adrenal glands can be measured at the time of ultrasound to determine if they are normal in size and shape. In addition, abdominal ultrasound may detect retained reproductive tissue (in females), prostatic enlargement (in males), or bladder abnormalities, which could be differential diagnoses for the clinical signs. On rare occasions, the adrenal glands of clinically affected ferrets may be normal in size and shape, especially early in the disease process. The ferret androgen panel includes validated assays for estradiol, androstenedione, and 17-hydroxyprogesterone. Most affected ferrets will have elevated blood level of one or more of these hormones.
Affected ferrets should have a thorough diagnostic workup because some of these animals have concurrent disease such as islet cell neoplasia and/or cardiac disease. In the majority of ferrets, results of a complete blood cell count and chemistry profile are within normal limits. Ferrets affected with adrenal disease can live with the hair loss. If the animal is not treated, however, the potential exists for urinary tract obstruction (in males), bone marrow suppression, tumor-related invasion of the vena cava, or metastasis.
Treatment options include surgical or medical therapy. Adrenalectomy (either unilateral or partially bilateral) is the treatment of choice because the affected tissue can be removed. Because of the intimate association of the right adrenal gland to the vena cava, a complete right adrenalectomy may not be possible.i If both glands are affected, then surgical therapy includes total resection of the largest gland and subtotal of the contralateral. Total bilateral adrenalectomy is not recommended because of the postoperative potential for hypoadrenocorticism to develop.
Research using cryosurgery has been reported, but no long term results have been published. Symptoms are often mitigated for some time after surgery, but clinical signs can recur. Clinical signs in treated patients usually resolve within two to four months of treatment.
Palliative medical treatment options currently being utilized include leuprolide acetate depot (Lupron Depot™, TAP Pharmaceuticals, Inc., Deerfield, IL), a synthetic, long-acting gonadotropin-releasing hormone (Gn-RH) analog.Leuprolide may also be useful for the treatment of prostatic hyperplasia, which often occurs in conjunction with the adrenal disease. Treatment with mitotane (Lysodren™ , Bristol-Myers Squibb Oncology, Princeton, N.J.) is effective in dogs for treatment of pituitary-dependent hyperadrenocorticism. This form of hyperadrenocorticism has not been recognized in ferrets and this treatment is rarely successful in ferrets. Destruction of the cortisol-producing cells can lead to clinical hypoglycemia if the ferret is subclinical for insulinoma.