Cushing's disease, or hyperadrenocorticism, occurs when a dog’s adrenal glands, located near the stomach and kidneys, overproduce the hormone cortisol. Cushing’s disease is most commonly found in elderly dogs, typically 6 years or older, but it can occur in a dog of any age. Some of the symptoms of Cushing’s disease are commonly associated with the natural aging process, which makes testing for the disease very important.
The pituitary gland produces an adrenocorticotrophic (ACTH) hormone, which is released into the bloodstream. This hormone tells the adrenal glands how much cortisol to produce to help the body handle daily stresses. The pituitary gland senses when there is enough cortisol in the blood, then stops producing ACTH in response. Small benign tumors in the pituitary gland cause the gland to ignore the levels of cortisol, allowing the overproduction. Small tumors in the adrenal glands can also cause them to overproduce cortisol, ignoring pituitary control, poisoning the bloodstream. Unfortunately, Cushing’s disease can also be caused by extended doses of corticosteroids.
As there is no known way to effectively prevent Cushing’s disease, it is crucial to perform diagnostic tests early enough to prevent further damage. As dogs reach middle-age, around five or six years old, more frequent visits to the veterinarian for blood tests may become necessary. There are several breeds that tend to suffer from Cushing’s, such as beagles, Boston terriers, boxers, dachshunds, and German shepherds, among others.
Cushing’s Disease Tests Explained
The Urine Cortisol/Creatinine Ratio Test can only rule out Cushing’s disease as a possibility, by comparing the excreted protein metabolite to normal levels. High cortisol levels in the urine may indicate high levels in the bloodstream, while balanced levels rule out Cushing’s disease. Many other conditions may cause false positives, rendering this test non-diagnostic.
The ACTH Stimulation Test first requires a blood sample. The dog is then injected with the hormone ACTH, stimulating the adrenal glands to produce cortisol. After a couple hours, blood cortisol levels are measured and compared to the original blood sample. A dog with Cushing’s disease has a greater elevation of cortisol. This test cannot provide information regarding whether the Cushing’s is pituitary or adrenal.
The Low Dose Dexamethasone Suppression Test is considered the best test to diagnose Cushing's disease. First, a blood sample is taken in the morning. The dog is then injected with a small dose of dexamethasone, a synthetic glucocorticoid, and samples are taken again at four hours and eight hours. Dexamethasone suppresses cortisol production in healthy dogs, but since a Cushingoid dog lacks the ability to do so, the cortisol levels remain the same. This test cannot provide information regarding whether the Cushing’s is pituitary or adrenal.
The High Dose Dexamethasone Suppression Test may be used to determine whether the dog has the pituitary or adrenal form of Cushing's. A blood sample is taken in the morning. The dog is then injected with a large dose of dexamethasone, and samples are taken again at four hours and eight hours. Adrenal tumors are indicated by zero suppression of cortisol, while pituitary tumors may still have some suppression ability.
Some common symptoms of Cushing’s disease include hair loss primarily on body, unusually thin skin, propensity for bruising, hard calcified lumps on skin, lethargy, swollen belly, increased appetite, thirst, and urination.Some less common symptoms are sudden difficulty breathing, weakness, panting, and stiff walking, possibly with paws knuckled over.
Treatment for pituitary dependent Cushing’s disease is often Lysodren or Mitotane, and Trilostane (aka Vetoryl). These are oral medications which are to be administered for the rest of the dog’s life. These medications work to suppress cortisol production in the adrenal glands. Treatment for adrenal dependent Cushing’s disease is often surgery to remove the tumor, sometimes in addition to Trilostane.
This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by,your veterinarian. Always seek the advice of your veterinarian or other qualified professional with any questions you may have regarding a medical condition. Never disregard or delay seeking professional advice due to what you may have read on our website.