Cushing’s Disease in Dogs

Cushing’s disease, also known as Cushing’s Syndrome or Hyperadrenocorticism, is an illness that results from excessive steroid hormone production in dogs.  

Symptoms  

At the time of diagnosis, most dogs are over 6 years old. The most common symptoms of Cushing’s disease in dogs include: 

• Increased thirst
• Increased urination
• Increased appetite
• Thinning hair coat
• Weakness or loss of muscle mass
• Pot-bellied appearance
• Skin changes including skin infections
• Urinary tract infections 

Cushing’s disease may also be suspected in patients with diabetes mellitus that is not responding to treatment as expected.   

Understanding Cushing’s Disease 

In a healthy dog, steroid hormones (cortisol) are produced by adrenal glands that sit above each kidney. The adrenal glands are stimulated by ACTH, a hormone released by the pituitary gland that’s located below the brain. The release of cortisol is tightly controlled to meet the exact needs of the body, including the ability to respond to stress and maintain normal homeostasis.   

There are several forms of Cushing’s disease in dogs, including: 

• The most common form (~85% of cases) results from a small tumor in the pituitary gland. This is called pituitary-dependent hyperadrenocorticism (PDH). 
  • In dogs with PDH, these tumors are most often small and not associated with any neurologic symptoms.   
  • For a smaller percentage of dogs with PDH, the tumor is larger (macroadenoma) and results in a combination of symptoms of Cushing’s and primary neurologic disease.    
• In ~ 15% of cases, Cushing’s disease is caused by a tumor in one of the adrenal glands. 
  • Tumors in the adrenal gland can either be benign or malignant (cancerous). 
  • Most dogs with adrenal tumors will have no symptoms other than the symptoms of their Cushing’s disease, particularly in the early stages.   
• Dogs can also develop symptoms of Cushing’s disease when they have been taking steroids for a long time. 
  • Most commonly, these steroids are prednisone or prednisolone.  
  • This is called iatrogenic Cushing’s and symptoms are expected to improve/resolve when the steroids are discontinued.  

Diagnosis 

Typically, pet parents observe signs of Cushing’s disease at home that prompt a visit to their family veterinarian, who then also notices changes during the dog’s physical examination and routine lab work.  

A formal diagnosis of Cushing’s disease requires additional blood work. Often, your family veterinarian will perform more specific diagnostics to evaluate adrenal function, including an ACTH stimulation test or a low-dose dexamethasone suppression test.    

If your dog is diagnosed with Cushing’s disease, your pet may require advanced diagnostics, such as:  

• An abdominal ultrasound can identify if your dog has a pituitary-dependent or adrenal-dependent form of the disease. This information can help determine the best treatment options for your dog’s specific case.  
• Advanced imaging (CT scan or MRI) is rarely needed but may be recommended if there is concern for a large pituitary mass.   

Treatment 

Most dogs with Cushing’s disease are treated with oral medications that work by reducing the production of cortisol from the adrenal gland. Medical management for Cushing’s disease requires life-long medications and routine monitoring with a veterinarian. Note that these medications can reduce symptoms of Cushing’s disease, but do not treat the underlying cause of the disease. 

• The most common and successful medications prescribed are trilostane (Vetoryl) or mitotane (Lysodren). 
  • It’s important to know that these medications have risks including the potential to: 
    • Suppress cortisol production too much 
    • Damage the adrenal gland, resulting in a condition called Addison’s disease.  
      • This is a potentially life-threatening complication that often manifests as a significant decline in appetite, vomiting, diarrhea, and dehydration. 
      • If your dog is being treated with medication for Cushing’s and has these symptoms, please have your dog evaluated immediately by a veterinarian.  

Other treatment options: 

• In rare cases when Cushing’s disease is caused by a larger pituitary tumor, radiation therapy or surgical removal of the pituitary gland may be an option for treatment.  
• Surgical removal of the adrenal gland may be an option if a primary adrenal tumor is the cause of the dog’s Cushing’s disease.  
  • Additional imaging such as an abdominal ultrasound or CT scan is often required to evaluate for:
    • The location of the adrenal tumor 
    • The presence of tumor invasion into the local blood supply 
    • Evidence of metastatic disease (tumor spread)  
  • Dogs with small, benign tumors that are successfully removed can be cured.  

Many patients with Cushing’s disease can return to an acceptable quality of life with appropriate treatment. If you are concerned that your pet may have Cushing’s disease, please reach out to your family veterinarian for further evaluation.   

Learn more about our Internal Medicine Service here. 

More Reading: 

• Tips for Managing a Pet with a Chronic Illness
• When Chronic Diseases Go South
• Five Veterinary Radiology Imaging Options for Pets