Cushing's Disease in Dogs
Hyperadrenocorticism in Dogs
The endocrine system is the collective system of organs that control hormones in the body, one of which is the cortisone hormone, responsible for protein and carbohydrate metabolism in the body. When a disorder of the body causes an excess of cortisone levels in the bloodstream, the metabolic process is hampered, leading to gastrointestinal disorders and hypertension, amongst other bodily disturbances. This condition is medically referred to as hyperadrenocorticism, and it is one of the most common endocrine disorders to affect dogs.
One of the causes is a tumor of the pituitary gland (the gland that controls all of the hormone production in the body). Hyperadrenocorticism can occur spontaneously due to a pituitary tumor, or, in 85 percent of cases, to enlargement of the pituitary gland.
Cushing’s disease refers specifically to an increase in cortisone due to a benign tumor of the pituitary gland. In 15 percent of cases, spontaneous hyperadrenocorticism occured as a result of cortisol-secreting adrenocortical cancer, half of all such adrenocortical cancers will metastasize (spread). Hyperadrenocorticism can also occur when veterinarians or other caregivers administer excessive amounts of glucocorticoids to pets for the treatment of low cortisone levels, inflammation, or allergies. This disease affects a number of bodily systems, and signs of this disease vary considerably between cases. However, the most common signs are related to the urinary tract or the skin. Hyperadrenocorticism generally affects middle-aged to older animals.
Symptoms and Types
The most common cause of hyperadrenocorticism is a benign (non-spreading) pituitary tumor. Malignant tumors of the pituitary, which metastasize through the body, are a less frequent cause for hyperadrenocorticism. An even less common cause is a tumor of the adrenal gland (adrenal tumor - AT), but when it does occur, it may be a benign tumor, or a malignant metastasizing tumor. Pituitary-dependent hyperadrenocorticism (PDH) includes tumors of the adrenal glands, as well as pituitary overgrowth.
Excessive glucocorticoid administration, which may be used for allergies, inflammation, or as a replacement therapy for low cortisone levels, can also cause hyperadrenocorticism in dogs.
Your veterinarian will perform a complete physical exam, including a blood chemical profile, complete blood count and a urinalysis. You will need to provide a thorough history of your pet's health leading up to the onset of symptoms.
Your veterinarian will also run tests to measure cortisone levels in your dog’s bloodstream. There are three tests for measuring cortisone which will help your veterinarian to diagnose hyperadrenocorticism: a urine cortisol creatinine ratio test, and two types of blood tests: a low-dose dexamethasone suppression test, and an adrenocorticotropin hormone (ACTH) stimulation test. Excess levels of the adrenocorticotropin hormone will be indicative of Cushing’s disease as the stimulus behind the increase in cortisone.
After your veterinarian has settled on a diagnosis of hyperadrenocorticism, there will need to be further tests to see if it is being caused by PDH related tumors, or overgrowth of the pituitary gland. The high-dose dexamethasone suppression test is a blood test that may conclusively point to PDH caused hyperadrenocorticism by measuring cortisone levels in response to administration of the anti-inflammatory agent dexamethasone. A lowered, or unchanged cortisol level in response to the test will indicate Cushing’s disease.
Another blood test, the endogenous ACTH concentration test can confirm an adrenal tumor (AT) as the cause of your pet’s hyperadrenocorticism.
X-ray and ultrasound imaging can show 50 percent of adrenal tumors, and can be quite helpful in differentiating PDH from AT. If a patient has an AT, chest radiographs and ultrasound images should be taken to visually examine the body for any possible metastasizing.
A medical condition involving excessive thirst
The gland that is found at the bottom of the brain whose job is to maintain appropriate levels of hormones in the blood
Anything that produces an action or reaction
An in-depth examination of the properties of urine; used to determine the presence or absence of illness
The occurrence or invasion of pathogens away from the point where they originally occurred
Something that becomes worse or life threatening as it spreads
Something that has its origin inside the body
Not being able to cause harm; the opposite of malignant.
The digestive tract containing the stomach and intestine
High blood pressure
The gland that produces the hormone adrenaline and others; helps to regulate the metabolism, electrolytes, and even sexual function; also helps to regulate the way the body responds to injury, trauma, etc. The adrenal gland is found near the kidney. Also referred to as the suprarenal gland.
The group of processes that involve the use of nutrients by the body
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