Cushing's Disease is a condition in dogs that occurs when the body produces too much of the hormone cortisol. Also called hyperadrenocorticism, there are two main forms of this disease:
- Pituitary-dependent (most common form): The pituitary gland in the brain overstimulates the adrenal glands, causing them to produce too much cortisol.
- Adrenal-dependent: the adrenal glands cause cortisol overproduction
A third form, iatrogenic hyperadrenocorticism, can occur if a dog had been treated with steroids at high doses or for a prolonged period of time.
Cushing's Disease is relatively common in dogs and somewhat common in horses. Cushing's can occur in cats and humans, though less commonly so.
Signs of Cushing's Disease
The signs of Cushing's Disease may be similar to the signs of other health problems, so it's important to see your veterinarian if your dog seems sick. The following signs are typically seen in dogs with Cushing's Disease:
- Increased thirst and urination
- Increased appetite (dogs often seem ravenous)
- Enlarged abdomen (a "pot-bellied" appearance)
- Hair loss/thinning, especially along the sides of the body
How Cushing's Disease is Caused
The exact cause of Cushing's Disease is not known (except for the iatrogenic form, which has external causes). Some dog breeds are predisposed to the disease, such as Boston Terriers, Boxers, Dachshunds, and Poodles.
Most dogs that develop Cushing's disease are older adults and early seniors.
Diagnosing Cushing's Disease
Your veterinarian will begin with a thorough examination. Based upon the exam finding and the history you provide, your vet will most likely recommend lab work. At first, most vets run a blood chemistry, complete blood count, and urinalysis.
Abnormalities in these tests such as increased liver enzymes, increased cholesterol, and dilute urine may indicate Cushing's Disease, and your vet will need to run more lab tests. Additional tests that may be needed to diagnose Cushing’s disease include:
- Urine Cortisol:Creatinine Ratio: This urine test is usually abnormal in dogs with Cushing's disease. However, further diagnostic testing is necessary in order to confirm Cushing’s Disease.
- Adrenocorticotropic hormone stimulation test (ACTH stim): A blood sample is drawn, then a hormone injection is given. Another blood sample is drawn one to two hours later to measure the body's response.
- Low-dose dexamethasone suppression test (LDDST) OR High-dose dexamethasone suppression test (HDDST): These eight-hour tests involve a blood sample, an injection of a steroid, then additional blood samples at timed intervals to measure the body's response. These tests may help your vet determine where the problem is in the pet’s body (pituitary vs. adrenal).
- Abdominal ultrasound or CT scan: An abdominal ultrasound allows the vet to see the adrenal glands and look for abnormalities. A CT scan will enable vets to see abnormalities of the pituitary gland (located at the base of the brain). These tests may help your vet learn if your dog has pituitary-dependent or adrenal-dependent hyperadrenocorticism.
The most common type of Cushing's Disease is the pituitary-dependent form. Adrenal-dependent hyperadrenocorticism is generally caused by one or more adrenal tumors. About half of the time, these adrenal tumors are benign (the other half are malignant).
Cushing's Disease Treatment
Medical treatment is typically effective for pituitary-dependent Cushing's Disease. A drug called trilostane is most commonly prescribed. Trilostane inhibits an enzyme that is involved in the body's production of cortisol. Inhibiting this enzyme inhibits the production of cortisol.
Other less commonly used medications include lysodren, ketoconazole, and l-Deprenyl (Anipryl).
In the case of adrenal-dependent Cushing's Disease, some of the above medications may be effective (though the drug protocols differ). However, exploratory surgery and sometimes removal of the affected adrenal gland may be warranted.
Dogs being treated for Cushing's Disease will need to visit the vet regularly to have recheck examinations and follow-up lab work.
If your dog has been diagnosed with Cushing's Disease, talk to your veterinarian about the pros and cons of the various treatment options.