Cushing’s Disease in Dogs
Named after Harvey Cushing, the neurosurgeon who first described the disease in humans, Cushing’s disease occurs when there is an excess production of the steroid hormone cortisol by the adrenal glands. In dogs, there are two major forms of this endocrine disease: the pituitary form in which the pituitary gland in the brain sends a signal to the adrenal glands to produce excessive levels of cortisol, and an adrenal form, in which the adrenal gland pumps out excessive amounts of cortisol, causing clinical signs of cortisol excess. Most dogs have the pituitary form of Cushing’s disease.
A third type of Cushing’s disease is seen when dogs are prescribed steroids such as prednisone to treat conditions like allergies. This form is known as iatrogenic Cushing’s disease.
Cushing’s disease is common in dogs but not in other species. It is most often seen in middle-aged to older dogs and in the following breeds:
- Boston Terriers
- Miniature Poodles
It is important to recognize and Cushing’s disease. If untreated, dogs may develop diabetes and severe infections
- Increased water drinking
- Increased appetite
- Increased liver blood tests
- Distended abdomen
- Skin infections
- Dark, discoloration of the skin
- Urinary tract infections
- Hair loss
- Skin calcification
- Easy bruising
Diagnosing Cushing’s disease can be a challenge, since not all tests will give a positive result even if the dog has Cushing’s disease. Testing is further complicated because dogs with diseases other than Cushing’s disease can test positive for Cushing’s disease.
Three common types of tests are used to diagnose Cushing’s disease in dogs and in some dogs, all three types may be necessary.
- measure excessive steroids in a urine sample
- stimulate adrenal production of steroids via administration of a synthetic pituitary hormone
- suppress adrenal production of steroids by administration of steroids
Ultrasound, CT scan and MRI may be useful to identify adrenal gland tumors or pituitary tumors.
Drug therapy In the United States, veterinarians use oral medications when adrenal surgery is not possible or for Cushing’s disease stemming from the pituitary gland. Drugs used to treat Cushing’s disease decrease cortisol production by inducing atrophy of the layers of the adrenal gland layers responsible for producing cortisol or by inhibiting synthesis of cortisol by the adrenal glands.
Surgery If an adrenal tumor is identified as the cause of Cushing’s disease, then surgery is the treatment of choice to remove the tumor which is the source of excessive steroid production. In Europe, Cushing’s disease caused by a pituitary tumor is treated with surgical removal of the gland.
Radiation therapy Large pituitary tumors, even those causing neurologic abnormalities, can be successfully treated with radiation therapy.
If steroid medications caused your dog to develop iatrogenic Cushing’s disease, your veterinarian may recommend a plan to slowly wean your dog off of the steroids and implement an alternative treatment.
There is no way to prevent Cushing’s disease from developing. If your dog is on steroids, it does not mean he will develop iatrogenic Cushing’s disease, but it is important to keep an eye on any side effects. If you notice anything out of the ordinary, it is always best to contact your veterinarian.