In the normal animal, the adrenal glands (located next to the kidneys) produce a hormone called cortisol. Cortisol, which the "natural" form of cortisone, has many effects on body systems and is necessary for normal body function. The release of cortisol is controlled by another hormone called ACTH, which comes from the pituitary gland on the underside of the brain. This whole system is delicately balanced, but can sometimes be disrupted. If the disruption causes the release into the bloodstream of too much cortisol, the result is "hyperadrenocorticism," also called Cushing's syndrome.
Cushing's syndrome has two main causes, the pituitary form and the adrenal form. In the pituitary form, the pituitary gland malfunctions and begins to release too much ACTH. This in turn causes the adrenal glands to release too much cortisol. Approximately 75 to 85 percent of animals with Cushing's syndrome have the pituitary form of the disease. In the adrenal form, one of the adrenal glands develops a cortisol-secreting tumor on it. In this case, the pituitary gland is normal. It is very rare for both adrenal glands to have tumors on them and it is also very rare for the pituitary and adrenal forms of Cushing's syndrome to occur in the same animal. Adrenal gland tumors can be either benign or cancerous. If an adrenal tumor is cancerous, the prognosis is poor.
Cushing's syndrome affects dogs and cats of any breed or sex and almost any age. It is most common, however, in middle-aged dogs (i.e., 7 to 9 years old) of the German Shepherd, Toy Poodle, Dachshund, and terrier breeds. The course of the disease is slow and progressive, so the symptoms can go unnoticed for a long time. The signs of Cushing's syndrome are many and they include excessive thirst, excessive urination, a ravenous appetite, an enlarged "pot-bellied" abdomen, hair loss, poor wound healing, skin problems, bruising easily, lethargy, weakness, increased panting, genital abnormalities, and reproductive problems. The diagnosis depends on the signs and symptoms plus the results of certain blood and urine tests. Sometimes radiographs and ultrasound examinations are required as well. It should be noted that not all patients with Cushing's syndrome will show all of the above signs and some patients will not show any signs, especially in the early stages of the disease. In addition to the above symptoms, Cushing's syndrome patients are predisposed to developing congestive heart failure, high blood pressure, abnormal blood clots (called thromboembolisms), neurological problems, and infections, especially bladder and kidney infections.
The treatment for Cushing's syndrome depends on the cause. With the pituitary form, treatment is with medications that are administered for life. Medical treatment requires periodic monitoring with physical examinations and blood tests. Treatment of the adrenal form usually involves surgical removal of the adrenal gland that has the tumor on it. With either form of Cushing's syndrome, the pet owner's decision to give treatment must be made carefully because treatment can be an involved process, is not always successful, and certain risks are involved. Therefore, a firm commitment on the part of the pet's owner is required if treatment is attempted. Although the prognosis for cats with Cushing's syndrome is considered guarded to grave, successful treatment in dogs is common. The lifespan after the diagnosis in dogs can be anywhere from a few days to more than ten years (the average is two to three years) depending on the dog's age and the form of the disease. Although spontaneous remission of the disease has been seen in dogs, this is rare. With successful treatment, the signs and symptoms often resolve, the potential risks of Cushing's syndrome complications can be reduced, the pet's lifespan can be extended, and the pet's quality of life can be improved.