Downeast Dog News


By Gail D. Mason, DVM, MA, DACVIM | Feb 01, 2019

Cushing’s disease is a common disease in canines, particularly in smaller breeds. The syndrome occurs when one or both adrenal glands produce an excessive amount of cortisol (related to cortisone) in the body. While this hormone is essential in the body, excess amounts cause symptoms such as increased thirst, urination, hunger, panting, weight gain, and a pot-bellied appearance. The symptoms are slowly progressive, causing many owners to assume that it’s part of natural aging. Uncontrolled disease can result in hypertension, diabetes mellitus, pancreatitis, increase risk of infection, hair loss, and orthopedic issues.

There are two naturally occurring types of Cushing’s disease: 1) adrenal-dependent; and 2) pituitary gland dependent. The adrenal glands are located just above the kidneys. The glands have two layers. The outer layer of tissue called the “cortex” produces hormones called glucocorticoids and mineralocorticoids. The inner layer, the “medulla,” produces epinephrine. Adrenal-dependent Cushing’s disease is a result of a tumor forming on the adrenal gland. This is the underlying cause in less than 15% of all dogs with the disease. Of those, about half of the tumors are benign. The tumor causes a direct overproduction and release of cortisol into the bloodstream. The preferred treatment (and potential cure) is surgical removal of the tumor, which has a fair to good prognosis when performed by an experienced surgeon in a hospital setting.

Pituitary-dependent Cushing’s disease: the pituitary gland is located at the base of the brain. It secretes a hormone called adrenocorticotropic hormone or ACTH. The hormone indirectly controls the adrenal glands’ output of cortisol. Cushing’s disease results when a very small (usually microscopic) tumor of the pituitary produces an abundance of ACTH. In turn, the adrenal glands enlarge to accommodate this increased demand for cortisol release. This is the cause of over 85% of all cases of Cushing’s disease in dogs.

Testing for Cushing’s Disease: Your veterinarian would base diagnostic testing on the medical history and observations that you provide. If there is suspicion of Cushing’s disease, a simple screening test can be performed on a urine sample. If this test is “negative,” your dog likely does not have the disease. If the test is “positive,” your dog may have the disease. Further testing such as a “low dose dexamethasone suppression test” and/or an abdominal ultrasound may be indicated.

Treatment for pituitary dependent Cushing’s disease: Because the pituitary gland is vital to the body and access to it is difficult, a medical approach to treatment is preferred. It can be highly successful but requires a good working relationship between veterinarian and client.

a) Lysodren ® or mitotane is a time-honored and effective drug for the control of this disease. The mechanism of action is to shrink the outer adrenal gland layer which then limits the output of cortisol. Treatment involves 5-8 days of daily dosing (induction phase) which is followed by a 2-3 times weekly dosing of the drug (maintenance phase). It is important to be in close contact with your veterinarian during this phase so that the dosage is titrated for effective control of your dog’s disease. Care must be taken to not overdose the drug, as this can cause serious (though reversible) consequences. Overall, the risk of treating is lower than the risk of progressive, untreated disease.

b) Trilostane ®: is a drug that is a synthetic enzyme-inhibiting drug which decreases cortisol production by the adrenal glands. It differs from mitotane in that it decreases cortisol production, but usually does not physically change the adrenal gland. It is not a cure but can be very effective in managing Cushing’s disease.

With appropriate treatment, most or all symptoms of Cushing’s disease can be reversed. Most dogs can be successfully managed for long periods of time, which makes treatment very rewarding for most owners.