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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

 

  • Increased thirst and urination (polydipsia and polyuria, respectively)
  • Increased hunger
  • Increased panting
  • Pot-bellied abdomen
  • Obesity
  • Fat pads on the neck and shoulders
  • Loss of hair
  • Lack of energy
  • Inability to sleep (insomnia)
  • Muscle weakness
  • Lack of a menstrual period
  • Shrinking of testicles
  • Darkening of the skin
  • Appearance of blackheads on the skin
  • Thin skin (from weight gain)
  • Bruising (from thin, weakened skin)
  • Hard white scaly patches on the skin, elbows, etc. (associated with the disease calcinosis cutis)

 

Causes 

 

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.

 

 

Diagnosis 

 

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.

 

 

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