Courtesy of Anna Meredith MA VetMB CertLAS DZooMed MRCV Royal[Dick] School of Veterinary Studies
Hyperadrenocortiscism occurs commonly in middle-aged ferrets in America; associated with adrencortical hyperplasia, adenoma or adenocarcinoma. Pituitary dependent hyperadrenocorticism has not been recognised in ferrets. Incidence in the United Kingdowm has not been reported but in the author's experience this condition is rare. Cases are occasionally seen in gerneral practice and may definitely diagnosed following surgical removal of the affected adrenal gland and histopathological confirmation.
A recent study conducted at Utrecht University found the incidence in the Dutch ferret population to be 0.55% with a strong correlation observed between the age of neutering and age at time of diagnosis (Shoemaker et al 2000). It has been speculated that the practice of early neutering, which is common place in America, may predispose towards the development of this condition in later life. Studies in certain mouse strains have shown that early gonadectomy can lead to development of nodular adrenocortical hyperplasia, possibly due to undifferentiated gonadal cells in the adrenal cortex beoming functional in response to gonad removal. Other possible reasons for the high incidence in America as opposed to the United Kingdom are differences in husbandry, diet and genetic diversity (the ferret population in America is inbred).
Clinical signs include bilateral symmetrical tail alopecia and vulval swelling in females. This should be differentiated from hyperoestrogenism which is more commonly encountered. Castrated males may show signs of male sexual behaviour. Partial or complete urthral obstruction secondary to prostatic hyperplasia may occur associated with hperadrenocorticism in male ferrets. Androgens are thought to stimulate prostatic hyperplasia, leading to stranguria. Hair is easily epilated and is lost progressively over the perineum, tail, flanks, sides and back. Over 30% of cases may be prurient. If very enlarged the abnormal adrenal gland may be palpated.
On haematological examination of severe cases, pancytopaenia may be evident. AST is frequently elevated on biochemistry. Abdominal ultrasonography is the most useful tool with visualisation of the englarged adrenal glands. Diagnosis is not based of serum cortisol levels, ACTH stimulation tests, or dexamethasone suppression tests, as in the dog, since these are often normal in clinically affected animals. The sensitivity and specificity of urinary cortisol/creatinine ratios still needs to be evaluated in ferrets, although this has been described for diagnosis of hyperadrenocorticism in ferrets. Since ferrets produce very little excess cortisol with this disease, it may not be a useful tool. Instead, plasma androgens, oestradiol or hydroxprogesterone levels may be raised (see table). It is recommended that all these steriod hormones be assayed for a definite diagnosis. A total of 0.3ml of serum is required. Concurrent diseases found in older ferrets include insulinoma, splenic englargement, prostatic hyperplasia, cardiac disease and lymphoma.
Treatment is either by surgical removal or long term medical therapy. Surgical removal is the preferred option. If both adrenal glands are grossly affected then removal of one and partial removal of the other is advocated (Weiss et al 1999). Post-operative corticosteroid therapy is not routinely given. In unilateral cases improvement is seen in 2 - 8 weeks, with complete recovery in 5 months.
Therapy of Ketoconazole is ineffective when given orally at 15mg/kg every 12 hours. Reports of leuprolide use ('leuprolide acetate depot 30d') indicate that at 100ug/kg subcutaneous injection every 21 - 30 days, this drug may be effective in management of this condition. A clinical response is seen after the third injection, with remission after 6 months. At this stage the interval between doses may be increased. Slow-release deslorelin acetate implants (3mg) also appears promising as a treatment to temporarily eliminate clinical signs and descrease plasma steroid hormone concentrations and may be a useful therapy for ferrets that are considered a high surgical or anaesthetic risk or where the owner does not wish to choose the surgical option.
|Endocrine Hormone||Reference Ranges/Value|
|Androstenedione (nmol/L)||0 - 15*|
|0 - 28*|
|Oestradiol (pmol/L)||30 - 80*|
|0 - 0.8*|
|Insulin (pmol/L)||35 - 250|
|Cortisol (nmol/L)||0 - 140*|
|Male: 13.0 - 106.9|
Female: 9.14 - 32.69
|Male: 0.007 - 0.012|
Female: 0.004 - 0.011
*Normal ranges from University of Tennessee Clinical