Cushing's disease, named after the first physician who reported it, is caused by an excess of cortisol in the body.  It is most common in middle-aged to older dogs, especially Poodles, Dachshunds, Boston Terriers, Boxers, and Beagles.

Because Cushing's disease is caused by an excess of cortisol in dogs, it is important to understand what it is.  Cortisol is a corticosteroid hormone that is involved in metabolism and response to stress.  It is produced by the adrenal glands, which are found on top of the upper part of the kidneys.  The adrenal glands produce cortisol in response to another hormone that is secreted by the pituitary gland.  The pituitary gland, which is found in the brain, is called the master gland because it secretes a number of hormones that act elsewhere in the body, telling other organs to release additional hormones.

A tumor in either the pituitary gland or the adrenal glands can lead to too much cortisol and Cushing's disease.  Common signs include excessive water drinking and urinating.  Dogs often develop a "pot-bellied" appearance because cortisol thins the muscles of the abdomen, allowing the belly to sag, as well as increases the size of the liver.  Other common signs include hair loss (symmetrical), skin rash, darkened or thickened skin, weakness, sluggishness, and wounds that don't heal well.

Diagnosis includes tests to measure blood levels of cortisol under various conditions.  Because a series of blood samples is needed on a defined schedule (every 1-2 hours), pets usually need to stay in the veterinary hospital for the day.

Treatment is aimed at decreasing the amount of cortisol in the body.  Medications are available that destroy part of the adrenal gland (and so decrease the production of cortisol), or that counteract the hormone sent out by the pituitary gland to prevent the adrenal glands from producing too much cortisol in the first place.

Cushing's disease can also develop in dogs that have had to be treated long-term with corticosteroid medications for other problems.  These medications act the same way that cortisol does, so their side effects include the same signs, ie, drinking a lot of water, urinating frequently, etc.  When corticosteroid medications have been given long-term, they must be discontinued gradually to give the body time to get used to properly regulating its metabolism again.  Your veterinarian will work with you on a program to gradually decrease your pet's dosage of corticosteroid medication.

 Q&A

What is Cushing’s disease?
Cushing's disease is a condition of dogs in which the adrenal glands produces too much cortisol, which is a hormone involved in metabolism and stress.  

What causes Cushing's disease?
This condition is usually caused by a tumor in either the pituitary gland or the adrenal glands.  The pituitary is the master gland that tells the adrenals to produce cortisol.  Cushing’s disease can also develop after long-term treatment with corticosteroid medications, which mimic cortisol.  

What dogs are most likely to get this condition?
Cushing’s disease is most common in middle-aged to older dogs, especially poodles, dachshunds, Boston terriers, boxers, and beagles.

How is the disease treated?
Treatment usually involves medications that destroy part of the adrenal gland (and so decrease the production of cortisol), or that counteract the hormone sent out by the pituitary gland, thereby preventing the adrenal glands from producing too much cortisol in the first place.

Written and reviewed by John A. Bukowski, DVM, MPH, PhD
and Susan E. Aiello, DVM, ELS