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What is Cushing’s disease?

Cushing’s disease is the symptoms caused by the body being exposed to elevated cortisol for an extended period of time. Cortisol is produced by the adrenal glands, which are located near both kidneys. The pituitary gland in the brain signals the adrenal glands to produce cortisol. In a normal animal, when the pituitary gland senses the cortisol levels are low, it sends a signal (ACTH) to the adrenal glands to produce cortisol. Similarly, when it senses that the cortisol levels are high, it can signal the adrenal glands to stop producing cortisol.

What are the clinical signs?

The average age for dogs with Cushing’s is 9-11 years old. Poodles, Dachshunds, beagles, boxers and terriers are more pre-disposed than other breeds. Common clinical signs include: increased drinking and urination, increased appetite, pot-bellied appearance, hair loss, thin skin, lethargy and panting.

What are the causes?

The most common type of Cushing’s is called Pituitary-dependent Cushing’s. It is due to small, often benign tumors on the pituitary gland. These tumors lead to overstimulation of the adrenal glands thereby resulting in an overproduction of cortisol. The second type of Cushing’s is called Adrenal-dependent Cushing’s. It is due to a tumor present on an adrenal gland that results in an overproduction of cortisol. The type of Cushing’s present can be determined by performing an abdominal ultrasound. The adrenal glands can be directly examined for evidence of a tumor or enlargement resulting in an Adrenal-dependent Cushing’s diagnosis.

How is it diagnosed?

Dogs who have Cushing’s will often have an increase in the enzyme alkaline phosphatase (ALP) in their blood. Their urine will likely be quite dilute because of increased water intake and they are more prone to urinary infections. The main diagnostic test that is performed if Cushing’s is suspected is called a Low dose Dexamethasone suppression test (LDDST). This test involves collecting a resting blood cortisol level, giving an injection of dexamethasone and then measuring the blood cortisol levels 4 and 8 hours post-injection. LDDST will detect Cushing’s in 90% of dogs.

How is it treated?

Surgery may be performed to remove the tumor present in Pituitary-dependent Cushing’s whereas Adrenal-dependent Cushing’s requires ongoing treatment and it cannot be cured. Ultimately, the goal of Cushing’s treatment is to see a decrease in or to resolve clinical signs. Vetoryl (Trilostane) is the medication used to treat Cushing’s. It works by blocking the enzyme essential in the production of cortisol.   

How is it monitored?

Cushing’s is monitored by performing a test called an ACTH (Adrenocorticotropic hormone) stimulation blood test. The test is performed by collecting a blood sample for serum before and one hour after administering an intravenous injection of the hormone. An ACTH stimulation will determine if the patient’s cortisol levels are well controlled on the current Vetoryl dose.

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