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.