Named in honor of the John’s Hopkin”s neurosurgeon, Harvey Cushing, who first proposed the disease in 1912, Cushing’s Disease is seen in humans, dogs, and sometimes cats. In all cases, the reasons for the disease are the same.
What Causes Cushing’s Disease?
Cushing’s Disease (or hyperadrenocorticism) is a condition where the adrenal glands secrete too much cortisol (cortisone). There are two adrenal glands, one located adjacent to each kidney, and they are responsible for producing a variety of hormones including cortisol and adrenaline. The pituitary gland in the brain tells the adrenal glands how much cortisol to make. Cushing’s disease is one of the more common chronic diseases diagnosed in older dogs. The disease is less common in cats.
Two Potential Causes For Cushing’s Disease
There are two reasons that the adrenal glands may produce excessive cortisol and lead to a case of Cushing’s Disease. The most common reason is that the pituitary gland is telling the adrenal glands to produce too much cortisol. In this form of Cushing’s disease, also known as pituitary-dependent hyperadrenocorticism, the adrenal glands are simply producing what they are told to by the brain. The primary medical concern to the pet is the effects of too much cortisol in the body. Excess cortisone in the body has a multitude of deleterious effects.
The second, and much less common, cause of Cushing’s disease is that a cancerous tumor of the adrenal gland is producing the excess cortisol. This form is also known as adrenal-dependent hyperadrenocorticism. These dogs will exhibit the same symptoms as dogs with pituitary-dependent Cushing’s described above. The cancerous tumor itself, however, is the most serious concern as the tumor will invade into surrounding blood vessels and eventually metastasize to other organs.
One of the most common symptoms of Cushing’s, occurring in about 70% of dogs, is increased urination. Cortisone causes the kidneys to produce a more watery urine and, therefore, the dog urinates more and consequently needs to drink more to prevent dehydration. These pets may have urine accidents in the house or may wake their owner during the night to go outside to urinate.
Cushing’s dogs may have a variety of other symptoms as well. Cortisone is also a weak immunosuppressant. Dogs with Cushing’s disease may have recurrent urinary tract or skin infections. Cortisone also causes muscle break-down; dogs with Cushing’s often have a sagging belly due to gravity pulling on weaker abdominal muscles. In addition, Cushing’s dogs may pant more and have a thinning hair coat. Because cortisone raises blood sugar, pets may become diabetic and need insulin therapy. Pets with Cushing’s are more prone to blood clots and embolism/stroke.
- Recurring urinary infections
- Sagging, pendulous belly
- Excessive panting
- Hair loss
- Increased thirst and/or diabetes
- Increased risk of blood clots and stroke
To diagnose Cushing’s disease, we start with running a blood chemistry, complete blood count, and urinalysis. These tests help rule-out other diseases, such as kidney disease and diabetes, that have similar symptoms. In Cushing’s dogs, these tests will typically show a dilute urine, elevation of certain liver tests and cholesterol, and changes in the types of white blood cells present in the blood. If Cushing’s disease is still suspected after running these tests, confirmation testing is needed. Often, we will perform a Dexamethasone Suppression Test (see video below). In this test, a small dose of cortisone is given to the dog and then the dog’s cortisone levels are measured over an 8-hour period. If the dog is able to stop making cortisol, the dog does not have Cushing’s disease. If the dog continues to make excessive cortisol, the dog is diagnosed with Cushing’s disease. Some dogs will then need to have additional blood testing or abdominal ultrasound performed to determine whether or not the dog the dog has an adrenal tumor.
The Dexamethasone Suppression Test explained
The decision to treat and the type of treatment depends on knowing which form of Cushing’s the dog has. In a pituitary Cushing’s dog with mild symptoms, some owners may elect to wait to treat until symptoms worsen or the dog develops diabetes. Dogs with symptoms are treated with medication, typically Trilostane or Lysodren, which decrease the amount of cortisol produced by the adrenal gland. Since the body needs small amounts of cortisol in order to function, giving too much medication can be life-threatening. Blood testing is needed, therefore, to determine that the pet is receiving an appropriate amount of medication, neither too little nor too much. Once the appropriate dose is determined for that individual pet, periodic testing is needed to ensure continued control of the disease.
Since adrenal tumors are cancerous, they are best treated by an oncologist with surgery and possibly chemotherapy to try to increase survival time. If surgery is not elected, the symptoms can be controlled with the same medications used to treat pituitary Cushing’s cases to help with the pet’s quality of life. Since adrenal tumors typically produce more cortisol than in pituitary Cushing’s, higher doses of medication are usually needed. Therefore, even if surgery is declined, it is still important to diagnose which form of Cushing’s the pet has in order to appropriately dose these medications as well as to accurately counsel owners as to their pet’s prognosis.
Dogs with pituitary Cushing’s disease can live for years if no serious complications occur. Treatment is usually recommended when symptoms are affecting the dog/owner’s quality of life. Speak to us if you suspect your dog may have Cushing’s.