Cushing’s syndrome, also called hyperadrenocorticism, refers to a disease when the adrenal glands produce an excessive amount of a hormone, cortisol (also referred to as cortisone). Cortisol, is a hormone produced by the adrenal glands that are located near the top of each kidney and is released in times of stress to prepare for a “fight or flight” situation. The effect of cortisol alters the metabolism by mobilizing fat and sugar stores in the body, in addition to retaining sodium and water for physical exertion. When the pet’s body is exposed to excessive cortisol concentrations for extended periods of time, systemic illness results.
In the normal pet’s body, the pituitary gland, located in the base of the brain, can detect when cortisol levels in the blood are declining and stimulates a substance, ACTH (adrenocorticotropic hormone), causing the adrenal gland to release more cortisol. When cortisol levels are appropriate, the pituitary gland stops its stimulatory message. The pituitary gland can be thought of as a ‘thermostat’ for cortisol, raising and lowering the blood levels of cortisol by ACTH secretion.
There are several different mechanisms that can lead to Cushing’s syndrome and treatments vary depending on the cause.
Pituitary Dependent Cushing’s syndrome is the most common cause of hyperadrenocorticism in dogs. Essentially, the pituitary gland grows a small tumor, generally too small to cause any trouble and is usually benign. The result is an overproduction of ACTH leading to increased production of cortisol and enlargement of both adrenal glands. Rarely, the tumor can grow large enough to compress the brain and cause neurological symptoms.
Adrenal dependent Cushing’s syndrome accounts for 15% of dogs with hyperadrenocorticism where an adrenal tumor is responsible for the over production of cortisol. The tumor is usually large enough to be seen on ultrasound or less commonly on radiographs and may be malignant. There is little or no production of ACTH from the pituitary gland and causes a small or atrophied opposite adrenal gland
Cushing’s syndrome can also result from long-term medication of cortisone derivatives, iatrogenic Cushing’s syndrome. These medications are prescribed for their anti-inflammatory properties, such as, allergic skin disease and degenerative arthritis. The pituitary receives the high steroid level from the medication and does not send stimulation to the adrenal glands and in time, the adrenal glands atrophy and are not able to release cortisol on their own. The effect on the glands can last three months after medication is discontinued. To allow the adrenal glands to respond appropriately, the medications are often prescribed in a decreasing (taper) dose and not stopped abruptly.
There are many clinical signs of Cushing’ syndrome in dogs, but the signs come on very gradually and are not usually recognized by the owners. Most commonly, excessive water drinking and urination are noted. Other common symptoms are: increased or ravenous appetite, pot-bellied appearance, muscle weakness, skin disease, excessive panting, protein in the urine and high blood pressure.
Cushing’s syndrome is uncommon in cats and clinical signs are similar. Cats with Cushing’s syndrome often times develop diabetes, where as in dogs only 10% develop diabetes. Diabetes in animals with Cushing’s syndrome is very difficult to control until the Cushing’s syndrome in managed properly.
Diabetes and Cushing’s syndrome share similar clinical signs (increased drinking, urination, appetite, lethargy) and uncontrolled diabetes can lead to complications that can cause increased cortisol levels and signs that are identical to Cushing’s syndrome. Testing and diagnosis of Cushing’s syndrome in a patient without diabetes can be complicated and even more complicated in a diabetic patient.
Routine blood and urine testing is important to your pet’s health and should be performed at least once yearly. Check out Petnostics for an easy and reliable at home urine test kit and share the results with your veterinarian.
Consult your veterinarian before making changes to any monitoring or treatments.
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