Cushing’s Disease in Dogs: Causes, Symptoms, and Treatment

What is Cushing’s Disease in Dogs?

Cushing’s disease in dogs is also known as hyperadrenocorticism. This is a condition where an excessive amount of cortisol is created. Cortisol is a ‘stress hormone’ that is produced by the adrenal glands. With this disease there may be an abnormality of the pituitary gland, which is the gland that stimulates the adrenal glands to produce cortisol, causing excessive production of cortisol by the adrenal glands. Alternatively, a problem within the adrenal gland can cause it to produce too much cortisol.   

What Causes Cushing’s Disease in Dogs?

Cushing’s in dogs is a condition that most often occurs later in life. Middle-aged or older dogs are most commonly affected between 7-12 years of age. Miniature Poodles, Boxers, Boston Terriers, Beagles, Staffordshire Terriers, and Dachshunds have a higher risk of developing Cushing’s disease. Female dogs also have an increased risk of developing this disease. 

What are The Types of Cushing’s Disease in Dogs? 

There are three causes (or types) of Cushing’s disease in dogs. In most cases (80-85%) of dogs with this condition, there is a benign tumor located within the pituitary gland (pituitary-dependent). This pituitary tumor causes the pituitary gland to overproduce hormones that stimulate the adrenal glands to create excess cortisol. The tumor commonly grows at the base of the brain and is typically small and benign. As time goes on, this tumor may grow leading to neurological signs in less than 20% of canine patients. 

Less commonly (<15%), dogs will have adrenal tumors which cause the overproduction of cortisol. This is called adrenal-dependent Cushing’s disease. These adrenal tumors may be benign or malignant. 

Finally, this may be considered iatrogenic. This term means that the disease is caused by medical treatment for another condition. The most common cause of iatrogenic Cushing’s syndrome in dogs is the excessive use of corticosteroids. 

What are The Symptoms of Cushing’s Disease in Dogs?

Dogs with this disease can have a variety of clinical signs that can range in severity. Some dogs may even have no obvious signs at all and the disease is found incidentally. 

The most common signs of Cushing’s disease in dogs are:

• Increased thirst
• Excessive urination
• Increased hunger
• Hair thinning or loss
• Excessive panting 
• Distended abdomen or pot-bellied appearance 
• Thin skin with a predilection for skin infections or increased oil production
• Recurrent urinary tract infections
• Vision changes or blindness
• Urinary incontinence 
• Hard plaques on the skin secondary to calcium deposits 

How Is Cushing’s Disease Diagnosed in Dogs?

Cushing’s Disease in dogs can be a challenging condition to diagnose as blood tests can be inconclusive. There is also potential for false positive test results. No single test is 100% accurate to diagnose this disease. 

There are usually a variety of tests recommended to help determine the underlying cause of your dog’s clinical signs. Urine and blood tests are often recommended to assess underlying organ function and screen for infections. An ACTH stimulation test is the most common diagnostic used to identify Cushing’s disease in dogs. 

Alternatively, a dexamethasone suppression test may also be used to diagnose Cushing’s disease. If this testing is inconclusive, repeated testing is generally recommended in three to six months if clinical signs remain. 

Additional diagnostic imaging considerations include abdominal ultrasound or magnetic resonance imaging (MRI) to visualize adrenal gland tumors versus pituitary tumors.   

What is The Treatment for Cushing’s Disease in Dogs?

The treatment of Cushing’s Disease in dogs is mainly dependent on the cause of the disease. Medical management of Cushing’s disease is often favored, but surgical removal of the tumor can also be considered and may be curative. 

Radiation therapy may also be a favorable option for dogs with pituitary-dependent Cushing’s disease, especially if they are showing neurologic signs. 

Common medications used to treat Cushing’s disease in dogs include trilostane or mitotane. Both of these medications interfere with cortisol production, therefore, careful monitoring is important to ensure cortisol levels do not decline too quickly. 

Many dogs will need an ACTH stimulation test every three to six weeks to assess control of their Cushing’s disease. 

If Cushing’s disease is considered iatrogenic, the current corticosteroid dose should be slowly weaned and discontinued if possible. 

How to Prevent Cushing’s disease in Dogs

In most cases, Cushing’s disease in dogs is not preventable. This is especially true if the condition is caused by a pituitary or adrenal gland tumor. Iatrogenic Cushing’s disease can be avoided by careful use of corticosteroid medications, especially with long-term use. 

Recent Advances in Cushing’s Disease in Dogs

Veterinary medicine is constantly growing and evolving and so is the knowledge regarding Cushing’s disease in dogs. More recently interest has been given toward the development of a screening tool to predict the likelihood of Cushing’s disease in dogs. 

Complications of the disease are also being discovered including the risk of systemic hypertension. Research has also proven that dogs with Cushing’s disease who are treated with low initial doses of trilostane live nearly twice as long as those who are untreated.