What is Cushing's syndrome?
Hyperadrenocorticism is an endocrine disorder caused by excessive production of cortisol by the adrenal gland (the adrenal cortex, which is the outer part of the gland), or administered medically.
Hyperadrenocorticism is quite rare in cats. Middle-aged and older cats are most often affected.
What are the causes of hyperadrenocorticism in cats?
There are three causes of Hyperadrenocorticism in cats:
- Iatrogenic Cushing's (Veterinary induced) - Iatrogenic Cushings is the result of too many corticosteroids (especially cortisol) given either orally, topically or by injection.
- Adrenal tumours - In adrenal hyperadrenocorticism, one or both of the adrenal glands ignore the ACTH signal and begin to produce excessive amounts of corticosteroids. This is usually the result of a benign or cancerous tumour. Approximately 50% of adrenal tumours are cancerous. This is known as adrenal dependent hyperadrenocorticism.
- Pituitary tumour (Cushing's Disease) - Micro tumours in the pituitary gland can lead to it producing excessive amounts of adrenocorticotrophic hormone (ACTH). ACTH stimulates the adrenal glands to produce too much cortisol. This is known as pituitary-dependent hyperadrenocorticism.
What is the adrenal gland?
The adrenal glands are located above the kidneys.
The outer layer of the gland, called the adrenal cortex, produces hormones including cortisol, DHEA, estrogen and testosterone. Cortisol is essential for life, it plays several important roles, some of which include; converting proteins into energy, releasing glycogen and has pronounced anti-inflammatory and immunosuppressive effects.
Cortisol opposes the actions of insulin and in more than 90% of cats with Cushing's syndrome also had concurrent diabetes mellitus. *
The inner portion of the adrenal gland is called the medulla and it produces epinephrine and norepinephrine (adrenaline), which during a stress response, raises blood glucose levels, blood pressure, and cardiac output.
What are the symptoms of hyperadrenocorticism in cats?
- Increased thirst (polydipsia) and increased urination (polyuria)
- Increased appetite (polyphagia)
- Enlarged abdomen
- Muscle wasting
- Hair loss (bilateral symmetrical hair loss)
- Thin skin which is easily damaged (fragile skin syndrome)
- Lethargy/decreased activity
How is hyperadrenocorticism diagnosed in cats?
Hyperadrenocorticism may be tentatively diagnosed if your cat has a history of long-term corticosteroid use, and upon clinical signs and physical examination of the cat.
Diagnostic testing may involve routine tests such as
- Complete blood count: This may show an increase in levels of white blood cells
- Biochemical profile may reveal low calcium levels, elevated cholesterol, elevated glucose, possible elevated alkaline phosphatase and liver enzymes.
- ACTH stimulation test: This test measures the ability of the adrenal glands to respond to a hormone known as adrenocorticotropic hormone (ACTH) which is made in the pituitary gland, travelling through the bloodstream to the adrenal glands where it stimulates the secretion of other hormones such as hydrocortisone from the cortex. The ACTH stimulation test measures levels of cortisol in the blood before and after an injection of synthetic ACTH.
- Low dose dexamethasone suppression test (also known as ACTH suppression test): This test can help distinguish between adrenal dependent hyperadrenocorticism (ADH) and pituitary-dependent hyperadrenocorticism (PDH). It measures the response of the adrenal glands to ACTH. Dexamethasone is a synthetic steroid (similar to cortisol) which suppresses ACTH. Dexamethasone is administered and blood cortisol levels are measured. Cortisol levels should decrease in response to the administration of dexamethasone.
- Urine Cortisol:Creatinine Ratio (UC:Cr): This tests levels of cortisol in the urine and is measured against levels of creatinine. If the level is normal, hyperadrenocorticism can be ruled out.
- Abdominal x-rays can be useful to check for enlarged adrenal glands, calcification of the adrenal glands or other organs and an enlarged liver (hepatomegaly).
- Ultrasound: This can enable the veterinarian to measure the adrenal glands.
- In the case of spontaneous hyperadrenocorticism, your veterinarian will need to establish which gland is causing the disease.
What is the treatment for hyperadrenocorticism in cats?
If the disease is caused by the use of corticosteroids then the medication will be gradually withdrawn. This needs to be done slowly and carefully to give the adrenal glands the chance to begin functioning properly.
Generally, while drugs have been shown to be effective in dogs, this is generally not the case in cats.
Surgical removal of the adrenal gland(s) (adrenalectomy). If the disease is caused by an adrenal tumour in one gland, then only the affected gland will be removed. If the disease is caused by a pituitary tumour then both the adrenal glands will be removed. Adrenalectomy is a risky and difficult operation, and once the adrenal glands are removed your cat will have to have replacement therapy with glucocorticoids and mineralocorticoids throughout their lives.
Your veterinarian will be able to best advise you on the latest treatment options.
*References: The Cornell Book of Cats.