Cushing’s Syndrome (Hyperadrenocorticism) in Cats

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    About: Cushing’s syndrome is a rare condition that occurs due to prolonged exposure to high levels of the hormone cortisol.

    Causes: Long-term use of corticosteroids, pituitary gland tumour or adrenal gland tumour.

    Symptoms:

    • Increased thirst and urination
    • Enlarged (pot) belly
    • Increased appetite
    • Muscle wasting
    • Bilateral hair loss
    • Thin skin
    • Lethargy

    Treatment:

    Gradual withdrawal of corticosteroids or surgery to remove the tumour.

    What is Cushing’s syndrome?

    Cushing’s syndrome (hyperadrenocorticism) is an endocrine disorder that occurs from prolonged exposure to high cortisol levels. While common in dogs, Cushing’s disease is rare in cats.

    Causes

    There are three causes of Cushing’s syndrome in cats:

    • Iatrogenic Cushing’s (veterinary induced): Iatrogenic Cushing’s is the result of the administration of too many corticosteroids (primarily cortisol) over a prolonged period.
    • Adrenal tumours: One or both of the adrenal glands ignore the ACTH signal and produce excessive amounts of corticosteroids due to a benign or cancerous tumour. Approximately 50% of adrenal tumours are cancerous.
    • 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 (pituitary-dependent hyperadrenocorticism).

    What is the adrenal gland?

    Adrenal gland
     Image Designua/Shutterstock

    The adrenal glands are located on top of the kidneys and consists of an outer and an inner layer.

    • Adrenal cortex:  The outer layer which produces hormones including cortisol, DHEA, estrogen and testosterone. Cortisol is essential for life; it plays several critical roles, which include converting proteins into energy, releasing glycogen and has pronounced anti-inflammatory and immunosuppressive effects. Cortisol opposes the actions of insulin and more than 90% of cats with Cushing’s syndrome also had concurrent diabetes mellitus.
    • Medulla: The inner portion of the adrenal gland and produces epinephrine and norepinephrine (adrenaline), which raise blood glucose, blood pressure and cardiac output during a stress response.

    Symptoms

    • Increased thirst (polydipsia)
    • Increased urination (polyuria)
    • Increased appetite
    • Enlarged abdomen due to hepatomegaly
    • Muscle wasting
    • Bilateral symmetrical hair loss
    • Thin and fragile skin
    • Lethargy/decreased activity
    • Non-responsive diabetes

    Diagnosis

    A suspicion of Cushing’s syndrome can be made if the cat has a history of long-term corticosteroid use as well as uncontrolled diabetes. The veterinarian will perform a complete physical examination and obtain a medical history from you.

    Diagnostic workup:

    • Complete blood count: A blood test that measures the cellular components of the blood (red blood cells, white blood cells and platelets, which may show an increase in levels of white blood cells.
    • Chemistry profile: A test on the clear/fluid portion of the blood which 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 the adrenocorticotropic hormone (ACTH), which is made in the pituitary gland. ACTH travels 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 (ACTH suppression test): A test to measure the ability of the adrenal glands to respond to the adrenocorticotropic hormone (ACTH), which is made in the pituitary gland. ACTH travels 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.
    • Urine Cortisol: Creatinine Ratio (UC: Cr): A test to evaluate how much protein is being lost via the kidneys by measuring protein and creatinine in a urine sample. Creatinine, a by-product of muscle metabolism, is normally excreted into the urine at a constant rate. Low levels of protein in the urine are normal, but high levels of protein are a sign of kidney injury/disease. The UPCR expresses the difference between the two values (protein, creatinine) as a ratio.
    • Abdominal x-rays: These 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.

    Treatment

    Treatment options will vary depending on the underlying cause of Cushing’s syndrome.

    • Iatrogenic: Gradual withdrawal of corticosteroids; it is important to taper withdrawal to give the adrenal glands the chance to begin functioning again.
    • Adrenal tumour: Surgical removal of the adrenal gland(s) (adrenalectomy) or medical management. Surgical removal is not without its risks, which include bleeding, and a sudden release of adrenal hormones, which can pose an anesthetic risk, therefore, the cat may be referred to a veterinary specialist centre.
    • Pituitary tumour: Surgical removal of one or both of the adrenal glands (adrenalectomy) which is a risky and challenging operation. Once the adrenal glands are removed, the cat will need replacement therapy with glucocorticoids and mineralocorticoids throughout their lives.

    *References: The Cornell Book of Cats.

    Author

    • Julia Wilson, 'Cat World' Founder

      Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio