Cushing’s disease is a syndrome that occurs in pets (and people) that is caused by an excess amount of cortisone (cortisol) being present in the body. Mammals normally produce the hormone cortisol in the adrenal glands. This hormone has a great number of functions in the body but is primarily concerned with helping the organism deal with stress. In the amounts normally produced in the body, cortisol is a very useful and beneficial hormone. In fact, neither you nor your pet can live without cortisol. The production of cortisol is under control by the brain. The pituitary gland is the primary controller of the cortisol levels in the blood. Under normal circumstances, the pituitary gland monitors the amount of cortisol in the blood. When the levels drop below a certain point, or when there is some stress confronting your pet, the pituitary gland sends a hormonal messenger; Adrenocorticotrophic (ACTH) hormone to the adrenal gland that tells it to make and release more cortisol into the blood stream. As the level of cortisol rises in the blood, the pituitary gland recognizes it and then stops sending the ACTH, which allows the adrenal gland to stop its release.
Cushing’s disease most commonly occurs when either the pituitary gland does not “listen” to the presence of cortisol in the blood, and continues to stimulate the adrenal glands (with ACTH) regardless of the amount of cortisol in the blood. . The failure to stop the ACTH release is caused by the presence of a small tumor in the pituitary gland that does not obey the rules that normal pituitary cells adhere to. These tumors are usually very small (about the size of a pea) and rarely cause brain damage. Unfortunately, they continue to stimulate the adrenal gland and so the body has to deal with the excess cortisol. In rare cases (10-15%, the pituitary tumor can grow large enough to put pressure on other parts of the brain. In these cases, the pet may experience blindness, disorientation, circling, seizures and other neurologic symptoms.
The second way in which Cushing’s disease develops is if there is a tumor growing out of one of the adrenal glands themselves. These tumors produce and release cortisol without listening to the pituitary gland. Fortunately, this type of tumor occurs in only 15% of the pets that develop Cushing’s syndrome. Fifty percent of these tumors are benign adenomas which only cause the problems associated with excess cortisol. The other 50% are malignant tumors called adenocarcinomas. Unfortunately, these tumors may spread to other parts of the body and eventually become fatal.
What are the symptoms of Cushing’s syndrome?
The symptoms of this disease are directly related to the effects of cortisone on the body. They include:
- Excessive Thirst
- Pendulous Belly
- Excessive urination
- Weight Gain
- Excessive Appetite
- Thin Hair and Skin
Is this disease dangerous?
Excessive cortisol in the blood can lead to suppression of the immune system, which can lead to excessive infections. It can also cause the pet to develop Diabetes Mellitus, High Blood Pressure (Hypertension), Strokes and Kidney Disease.
How do our veterinary team diagnose this disease?
There are a number of tests used to diagnose Cushing’s disease. None of the available tests can detect Cushing’s disease with 100% accuracy. Generally, each test has about an 85% accuracy level. That means that if one test is negative, but we still suspect that your pet has this disease a second test might be warranted. We generally start with an 8-hour test called the Low Dose Dexamethasone Suppression Test. In this test we take a sample of blood in the morning, then give your pet an injection of a type of cortisone called dexamethasone. In normal pets, this injection will cause the body to stop producing cortisone for about 8 hours. In pets that have Cushing’s syndrome, the level of cortisol in the blood will rise by the end of the test.
An alternative test is the ACTH stimulation test. In this test, we take a blood sample to measure the resting cortisone level. Then we inject ACTH hormone. 1-2 hours later we take another sample. Normal dogs will rise only so high in response to the ACTH while dogs with Cushing’s will send their cortisol levels up beyond a certain level.
If either of these tests is abnormal, we then may have to do a second test (High dose dexamethasone suppression) test to tell if the problem is being caused by the Pituitary Gland or an Adrenal tumor.
How do our veterinarians treat Cushing’s syndrome?
There are a number of options for treatment of this disease. We will select the drug based on the severity of the problem, the size of the pet and the costs of maintaining your pet on the drugs.
How successful is the treatment?
For most of the pets of Alta Loma, Rancho Cucamonga, Upland, Ontario, Claremont, Fontana and the Inland Empire that have pituitary dependant Cushing’s syndrome (85% of the pets), the treatment is usually quite successful. These dogs should be able to live pretty normal lives. They will need periodic monitoring and slightly closer oversight than a non-cushingoid pet. Those pets who have an Adrenal tumor do not have nearly the same prognosis. These tumors do not readily respond to drug therapy and surgical intervention is rather risky since the adrenal gland tumors tend to grow into the vena cava.
If you have any questions about this topic or any aspect of your pet’s health care, please feel free to ask our doctors and call (909) 980-3575.