This information is not meant to be a substitute for veterinary care. Always follow the instructions provided by your veterinarian.
Cushing's disease (hyperadrenocorticism) is the overproduction of the hormone cortisol by the adrenal glands that are located in the belly near the kidneys. Cushing's disease occurs commonly in dogs, but is rare in cats. Most dogs with Cushings disease are about 6 years old or older but sometimes Cushing's disease occurs in younger dogs. Cortisol affects the function of many organs in the body, so the signs of Cushings disease may be varied. Some of the more common signs of Cushings disease include hair loss, pot-bellied appearance, increased appetite, and increased drinking and urination called polydipsia and polyuria (PU/PD). Hair loss caused by Cushings disease occurs primarily on the body, sparing the head and legs. The skin is not usually itchy as it is with other skin diseases. If you pick up a fold of skin on a dog with Cushings disease, you may notice that the skin is thinner than normal. The pet may have fragile blood vessels and may bruise easily.
Less common signs of Cushings disease are weakness, panting, and an abnormal way of walking (stiff or standing or walking with the paws knuckled over). Some dogs with Cushings disease develop a blood clot to the lungs and show a rapid onset of difficulty breathing.
Dogs that are given prednisone or similar drugs can develop signs that look like Cushings disease (called iatrogenic Cushings).
There are two types of Cushings disease:
pituitary- dependent and adrenal- dependent
There are two types of Cushings disease that are treated differently. The most common form of Cushings disease is caused by the overproduction of a hormone by the pituitary gland in the brain that in turn controls the amount of cortisol produced by the adrenal glands. This is called pituitary-dependent Cushings. A small percentage of dogs with Cushings disease have a tumor of one of the adrenal glands which is called adrenal-dependent Cushings.
There is no single test to diagnose Cushings disease. The history, physical exam, and results of initial blood and urine tests often provide a strong suspicion for the presence of Cushings disease. Laboratory tests that are most commonly altered by Cushings disease are an increase in white blood cell count, increase in the liver enzyme ALP (also called SAP or serum alkaline phosphatase), increased blood sugar (although not as high as the blood sugar levels of diabetic patients), increased cholesterol and dilute urine. See What Do Those Lab Tests Mean? for additional information about laboratory tests.
The large amount of cortisol in the body suppresses the immune system and allows the pet with Cushings disease to get bacterial infections. The most common location for infection is the bladder. Pets with Cushings disease may have a silent bladder infection meaning they dont show signs of having the infection such as straining to urinate. A culture of the urine may be necessary to diagnose the infection.
Specific tests for Cushings help confirm the diagnosis and determine type X-rays of the belly often show a large liver. Occasionally the x-ray will show calcium in the area of one of the adrenal glands that is suggestive of an adrenal tumor. Ultrasound of the belly may show enlargement of both adrenal glands in pets with pituitary-dependent Cushings or enlargement of just one of the adrenal glands in pets with an adrenal tumor. The adrenal glands are NOT always seen during an ultrasound exam in pets with Cushings. In some pets with an adrenal tumor, the tumor can be seen growing into large blood vessels close to the adrenal gland or spread from the tumor may be seen in the liver.
Specific tests for Cushings disease are performed to confirm the diagnosis and to determine the type of Cushings disease that is present, pituitary-dependent, or adrenal-dependent. Specific tests for Cushings disease have varied results. In some cases the results are clear cut and the diagnosis is made, but in other cases the test results are not clear cut and a series of tests must be performed. Some of the specific tests for Cushings disease include urine cortisol/creatinine ratio, low dose dexamethasone suppression test, high dose dexamethasone suppression test, and an ACTH stimulation test.
Treatment for Cushing's depends upon the type The treatment of the most common type of Cushings disease (pituitary-dependent) is lifelong oral medication. The most common drug used to treat Cushings disease is o, p-DDD(also called Lysodren® or mitotane). Occasionally ketoconazole or L-Deprenyl® is used to treat Cushings disease. o, p-DDD is initially given daily or twice daily for about a week (sometimes more, sometimes less). The initial treatment is called induction. o, p-DDD can have serious side effects, so pets being treated for Cushings disease must be closely watched. After induction o, p-DDD is given less often, usually once or twice weekly for the life of the pet. Some pets will have a recurrence of signs of Cushing's disease later in life, even though they are receiving o, p-DDD.
Treatment of adrenal dependent Cushings disease is by surgical removal of the cancerous adrenal gland. Adrenal gland tumors can spread to other parts of the body in which case all the cancer cannot be removed by surgery. Drugs such as o, p-DDD or ketoconazole are often given before surgery to reduce hormone levels before surgery. o, p-DDD is not as effective in reducing signs in pets with adrenal-dependent Cushings disease as it is in pets with pituitary-dependent Cushings disease.
The prognosis for pituitary-dependent Cushings disease with treatment is usually good. Some signs will disappear quickly and others gradually. Appetite and water consumption usually return to normal in a few weeks where as full return of the fur may take several months.
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