Cushing’s disease is a common hormonal disorder that affects middle-aged and older dogs (this condition is rare in cats).
The symptoms are caused by an excess of corticosteroid in the bloodstream, which causes increased thirst, thin skin, a potbelly and other signs. The majority of cases are the result of cortisol-producing glands (the adrenal and pituitary glands) becoming overactive, whereas a small proportion are caused by tumors of these glands.
Certain breeds are at increased risk of developing Cushing’s disease including the Beagle, Boston Terrier, Boxer, dachshund and poodle. The treatment is to take a daily capsule containing trilostane; although therapy is effective in most cases, the medication is expensive.
Many people mistake the signs of Cushing’s disease for those of old age. The dog gradually slows down, is less energetic and sleeps more.
Other common symptoms include:
- Weight gain
- Sagging stomach that takes on a potbellied appearance
- Dull and sparse coat
- Thin skin with blackheads
- Increased thirst, which increases water intake, resulting in possible lapses in toilet training
Another unfortunate consequence of Cushing’s is a high proportion of dogs developing high blood pressure. This makes an unexpected vascular incident, such as a stroke, more likely. Indeed, experts in the field believe the high blood pressure associated with Cushing’s disease is the biggest single cause of sudden, unexplained death in older animals.
This video shows “Peggy dog,” a dog whose shaking is a result of Cushing’s disease:
Cushing’s is caused by an increase of the secretion of hormones that stimulate the body to manufacture natural steroids.
These steroids are essential to help the pet cope with everyday stresses, but a constant high level leads to clinical signs such as thirst and a potbelly. An error in hormone production can originate from the pituitary gland in the brain or the adrenal gland next to the kidney. Around 85 to 90% of cases are due to overactivity of these glands, with the remainder due to tumors.
Another form of Cushing’s is “iatrogenic” or “induced by medication.” This may happen if the patient is given high doses of oral steroids for a long time. The effect of the drug is the same, as if the body made the steroid, and in some cases clinical signs develop.
Your vet will discuss the risks of steroid medication with you should your dog require high doses to treat another medical condition.
The veterinarian may suspect Cushing’s from the history and certain changes on a routine blood panel. However, a definite diagnosis must be made before starting treatment.
A special “stimulation” blood test can give the answer.
There are 3 types of tests available, each looking at a slightly different point in the production line for steroid.
Unfortunately, though these tests are excellent, no one test is 100% foolproof; false negative or positives do occur. If your veterinarian thinks the test is not a true reflection of what he suspects, then it may be necessary to run a second type of test to check out a different part of the steroid manufacturing process.
If test results point toward an adrenal tumor, then an ultrasound scan of the kidney and adrenal gland is appropriate to look for signs of cancer.
The majority of cases respond to a once-daily oral treatment with trilostane (Vetoryl). Those that do not respond are more likely to have a tumor. If the tumor is located in the adrenal gland, then surgery can be curative; however, this is a tricky operation best undertaken at a specialist facility.
Once the dog is stabilized on trilostane, his blood pressure should be monitored. If it is high despite treatment, then adding in anti-hypertensive medication is essential to decrease the risk of sudden blindness or a stroke.
There is no known method of preventing Cushing’s disease except for those iatrogenic cases induced by steroid medications. In these cases, giving the steroid tablet on alternate days somewhat decreases the body’s dependence on the steroid and reduces the risk of inducing Cushing’s disease.
- “Hyperadrenocorticism.” Peterson. Current Veterinary Therapy. 1986. Publisher: W. B. Saunders.
- “Hyperadrenocorticism (Cushing’s disease).” Tilley & Smith. The Five-Minute Veterinary Consult. Publisher: Williams & Wilkins.
This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Dec. 4, 2014.