Cushing's disease, known medically as hyperadrenocorticism, is a condition in which the adrenal glands produce an excess of cortisol. Cortisol is a vital hormone that helps regulate metabolism, blood sugar, immune function, and the body's response to stress. However, when produced in excess over a prolonged period, cortisol causes widespread damage to virtually every organ system in the body.

There are three forms of Cushing's disease in dogs:

• Pituitary-dependent (PDH): This accounts for approximately 80-85% of all Cushing's cases. A small tumor, almost always benign, develops on the pituitary gland at the base of the brain. This tumor sends excessive signals to the adrenal glands, causing them to overproduce cortisol. Because the tumor is usually very small, it rarely causes neurological symptoms on its own.
• Adrenal-dependent: In about 15-20% of cases, a tumor develops directly on one of the adrenal glands. These tumors can be benign (adenoma) or malignant (carcinoma). The tumor produces cortisol independently, without signals from the pituitary gland.
• Iatrogenic: This form is caused by the long-term administration of steroid medications (such as prednisone) for other conditions. The external steroids mimic the effects of excess cortisol. This form resolves when the steroid medication is gradually tapered and discontinued under veterinary guidance.

Cushing's disease is most commonly diagnosed in middle-aged to older dogs, typically between 8 and 12 years of age. Breeds with higher incidence include Poodles, Dachshunds, Boston Terriers, Boxers, Beagles, and Yorkshire Terriers. It develops slowly and progressively, and many owners initially attribute the changes to normal aging, which often significantly delays diagnosis.

The symptoms of Cushing's disease develop gradually, often over months or even years. Because the changes are slow and many overlap with normal aging, Cushing's is frequently one of the more difficult conditions for owners to recognize early. However, the combination of several hallmark symptoms together should prompt veterinary investigation.

The most common symptoms include:

• Excessive drinking and urination: This is often the first sign owners notice. Dogs with Cushing's may drink two to ten times their normal water intake and need to go outside much more frequently. Housebroken dogs may begin having accidents indoors.
• Increased appetite: Many owners describe their dog as suddenly ravenous, begging for food constantly, getting into the trash, or stealing food they never showed interest in before.
• Pot-bellied appearance: Cortisol causes redistribution of body fat to the abdomen and weakening of the abdominal muscles, giving the dog a characteristic swollen, pendulous belly.
• Hair loss and skin changes: Symmetrical hair thinning or loss, particularly on the trunk and flanks, is common. The skin may become thin, darkened, or prone to bruising and infections. Some dogs develop hard, mineralized patches in the skin (calcinosis cutis).
• Muscle weakness and lethargy: Excess cortisol breaks down muscle protein, leading to weakness, exercise intolerance, and a general decrease in activity.
• Panting: Excessive panting, even at rest, is very common due to the effects of cortisol on respiratory muscles and fat distribution.
• Recurrent infections: Cortisol suppresses the immune system, making affected dogs prone to urinary tract infections, skin infections, and other opportunistic problems.

If your dog is showing several of these signs, particularly the combination of excessive drinking, increased appetite, and a pot-bellied appearance, ask your veterinarian to test for Cushing's disease. Diagnosis involves specific blood tests such as the low-dose dexamethasone suppression test (LDDS) and the ACTH stimulation test, along with abdominal ultrasound to visualize the adrenal glands.

Treatment for Cushing's disease depends on the underlying cause and the severity of symptoms. The goal of treatment is to reduce cortisol levels to a normal range, alleviating symptoms and preventing complications.

For pituitary-dependent Cushing's (the most common form):

• Trilostane (Vetoryl): This is the most commonly prescribed medication. Trilostane works by blocking an enzyme needed for cortisol production, effectively reducing cortisol output from the adrenal glands. It is given once or twice daily with food and requires regular monitoring through ACTH stimulation tests to ensure the dose is appropriate. Most dogs show noticeable improvement within the first few weeks of treatment, with reduced drinking, urination, and appetite.
• Mitotane (Lysodren): An older medication that selectively destroys the cortisol-producing layers of the adrenal glands. It is effective but requires careful monitoring because it carries a higher risk of side effects, including potentially destroying too much adrenal tissue (leading to Addison's disease).
• Radiation therapy: For dogs with larger pituitary tumors that are causing neurological signs, radiation therapy can help shrink the tumor.

For adrenal-dependent Cushing's:

• Surgery (adrenalectomy): Surgical removal of the affected adrenal gland can be curative if the tumor is benign and has not spread. This is a major surgery best performed by a board-certified veterinary surgeon.
• Medical management: If surgery is not an option due to tumor characteristics, the dog's health, or financial constraints, trilostane can be used to manage symptoms medically.

Treatment is lifelong for most dogs with Cushing's disease. Regular monitoring, typically every 3-6 months once the dog is stabilized, is essential to ensure the medication dose remains appropriate. Cortisol levels that drop too low can cause an adrenal crisis, which is a potentially dangerous condition known as iatrogenic hypoadrenocorticism or Addison-like syndrome, so close communication with your veterinarian is important. If your dog shows sudden lethargy, vomiting, diarrhea, or loss of appetite while on Cushing's medication, contact your veterinarian immediately, as these may be signs that cortisol has dropped too low and the dose needs adjustment.

With appropriate treatment, the prognosis for dogs with Cushing's disease is generally favorable. Most dogs experience significant improvement in their symptoms within the first few weeks to months of starting medication. The excessive drinking and urination typically improve first, followed by gradual improvements in energy, appetite, coat condition, and muscle strength.

Average survival times with treatment are approximately 2-3 years from diagnosis, with many dogs living longer. Factors that influence prognosis include the type of Cushing's (pituitary vs. adrenal), the dog's age and overall health, how well the condition responds to medication, and whether complications develop.

Complications to watch for during treatment include:

• Diabetes mellitus (which can develop concurrently with Cushing's)
• Urinary tract infections (regular urine screening is recommended)
• High blood pressure
• Blood clots (hypercoagulability)
• Signs of adrenal insufficiency from over-treatment: lethargy, vomiting, diarrhea, weakness, or collapse

Some owners choose not to treat Cushing's disease, particularly in very old dogs with mild symptoms or dogs with other significant health problems. This is a valid choice. Untreated Cushing's is not immediately life-threatening, and the symptoms progress slowly. However, without treatment, the chronic excess cortisol does increase the risk of serious complications over time, including diabetes, infections, and blood clots.

Whether you choose to treat or monitor, the most important thing is your dog's daily comfort and happiness. Many dogs with well-managed Cushing's disease continue to enjoy walks, meals, playtime, and the simple pleasures that make a dog's life full. Because Cushing's disease can also predispose dogs to diabetes and pancreatitis, maintaining regular veterinary checkups is essential to catch any secondary conditions early. Your veterinarian can help you find the right balance of care that gives your companion the best quality of life possible.