By Mindy Cohan, VMD
Cushing’s disease is a common endocrine (hormonal) problem that primarily affects middle-aged and senior dogs. It is also known as hyperadrenocorticism because the basis of this disease is the excessive production of cortisol (which plays vital role in carbohydrate, protein and fat metabolism) by the adrenal glands. These glands, which produce many hormones in a dog’s body, are small organs located just above both kidneys.
There are two forms of Cushing’s disease in dogs. The more common type, pituitary-dependent, accounts for 80 to 85 percent of cases. The adrenal-dependent form is seen in 15 to 20 percent of dogs diagnosed with Cushing’s. Each form occurs secondary to tumors of either the pituitary gland, a pea sized organ situated below the base of the brain, or the adrenal glands. Pituitary tumors are typically benign while approximately half of adrenal tumors have the potential to spread elsewhere in the body.
Both forms of Cushing’s disease manifest with similar symptoms, including:
An increase in water consumption and increased volume and frequency of urination is one of the most universal symptoms and is also usually the first sign of Cushing’s disease noticed by dog parents. This indication of Cushing’s occurs gradually, but dog parent’s begin to realize an abnormality when they must refill water bowls far more often than usual. Pet parents are prompted to call a veterinarian when they notice urinary accidents or a dog’s increased need to eliminate outside.
Pet parents may also notice an increase in appetite in dogs with Cushing’s disease. Dogs that previously grazed on kibble throughout the day may begin to eat an entire meal immediately or attempt to access food in a kitchen trashcan or on a countertop. Because many pet owners associate a poor appetite with illness, many assume that dogs with hearty appetites are the picture of health. This accounts for why, despite other behavioral and physical changes, some pet parents of dogs with Cushing’s delay evaluation by a veterinarian.
Dogs pant for many reasons such as cooling themselves, anxiety, pain and various medical problems such as anemia. The basis for increased panting in dog’s with Cushing’s disease is multifactorial. First, Cushing’s disease results in increased fat deposits in the abdominal cavity and around the chest. Second, an increase in liver size impedes the diaphragm from being able to expand with ease. Finally, excessive cortisol causes the muscles of respiration to become weakened.
Elevated cortisol levels cause systemic muscle weakness which can manifest as generalized lethargy. As the muscles of the abdominal wall lose strength, dogs develop a protruding belly. A pot-bellied appearance is exacerbated by an enlarged liver and the redistribution of fat within the abdominal cavity. Breeds with short legs, such as Dachshunds, may require protective clothing as their bellies begin to contact the ground.
Several endocrine disorders share the common symptoms of changes to the skin and hair coat. When Cushing’s disease is suspected, your dog’s veterinarian may also investigate conditions such hypothyroidism and sex hormone disorders. All three conditions manifest with thinning of the hair coat known as alopecia. The pattern, which affects the trunk of a dog’s body, is bilaterally symmetrical with the head and extremities being spared. Fur that was once lustrous gradually becomes dry, dull and brittle.
The effects of excessive cortisol also lead to skin that becomes thin and more prone to bruising and infection. Skin infections can arise spontaneously and wound healing is delayed. The development of calcium deposits in the skin (called calcinosis cutis) is another dermatologic manifestation of Cushing’s disease. The calcium deposits often develop around the head and neck or on the dorsum (back), groin and pads of a dog with Cushing’s disease. The infiltration of calcium within the skin causes the formation of firm plaques. These abnormal areas are prone to ulceration and often require medical treatment. A skin biopsy is necessary to definitively diagnose calcinosis cutis.
If you observe the aforementioned symptoms, schedule a consult with your dog’s veterinarian. The diagnosis and subsequent treatment of Cushing’s disease is important for maintaining your dog’s health and quality of life as well as preserving the human-animal bond. Unfortunately, many pet parents become frustrated and annoyed as their dog begins to have urinary accidents or needs to be walked additional times during the day and in the middle of the night. Treating Cushing’s disease will furthermore reduce the risk of high blood pressure, urinary tract infections and life threatening blood clots.
There are several tests available that are used as diagnostic tools for Cushing’s disease. The tests include analysis of urine and blood samples as well as abdominal ultrasound. Often, a combination of tests is done to support a diagnosis.
The treatment of Cushing’s disease depends on whether diagnostic tests indicate a pituitary or adrenal tumor. For pituitary based disease, the medications Trilostane and Mitotane are most commonly used. In cases of large pituitary tumors, surgery or radiation may be considered if the dog is exhibiting neurologic problems.
Since adrenal tumors have the potential to be malignant, evaluation for evidence of metastasis is needed. If tests indicate the spread of disease has occurred, a veterinary oncology consult is recommended. If there are no signs of metastasis, it does not definitively rule out the tumor’s dissemination. Adrenal tumors can be treated both medically and surgically. Due to the anatomical position of the adrenal glands, surgery can be very difficult and unpredictable. Pet owners should consult a board-certified veterinary surgeon to discuss the benefits and risks of surgery.
Cushing’s disease is a chronic condition that necessitates long term care and monitoring tests. Familiarity with the symptoms enables dog parents to recognize the early warning signs and seek prompt treatment. With appropriate care, dogs with Cushing’s disease can lead long and happy lives.
Learn more about how to treat Cushing’s disease in dogs.