By Jennifer Coates, DVM
Cushing’s disease, or hyperadrenocorticism, is caused by the overproduction of the hormone cortisol or overuse of corticosteroid drugs like prednisone. Read more to learn the causes, symptoms and treatment options for dogs with Cushing’s Disease.
- Medications: Dogs with Cushing’s disease caused by a tumor in their pituitary glands are generally treated with either mitotane (also called Lysodren) or trilostane.
- Surgery: Cushing’s disease that is caused by a tumor in the adrenal gland is best treated by surgically removing the tumor.
What to Expect at the Vet’s Office
If your pet has been diagnosed with Cushing’s disease, your veterinarian will need to determine which of two forms of the condition is to blame. A usually benign tumor of the pituitary gland within the brain is responsible in most cases (80-85%). The remainder of dogs (often larger breeds) have a tumor on one of their adrenal glands within the abdomen.
Adrenal tumors can be benign or malignant. A high-dose dexamethasone suppression test and/or abdominal ultrasound are the most common ways to differentiate adrenal-dependent from pituitary-dependent cases of Cushing’s disease.
Appropriate treatment for Cushing’s disease depends on a dog’s symptoms and whether the adrenal or pituitary form of the disease is to blame:
- Dogs with mild symptoms of pituitary-dependent Cushing’s disease often do not require treatment. They should be closely monitored for a worsening of their condition, at which time treatment can be started.
- The oral medications mitotane or trilostane are given to suppress the body’s production of the hormone cortisol once unacceptable symptoms of pituitary-dependent Cushing’s disease are present. The appropriate dose is determined by a dog’s response to the medications, but lifelong treatment will be required. Both drugs can have potentially serious side-effects, so dogs need to be closely monitored at home and tests run in the veterinary hospital on a regular basis.
- Dogs with adrenal-dependent Cushing’s disease are often put on mitotane or trilostane for 2-4 months to shrink the tumor, after which an experienced veterinary surgeon removes it. If surgery is not an option, treatment with mitotane or trilostane will allow some dogs to live happily, usually for a few months, before their quality of life becomes unacceptable.
What to Expect at Home
If you and your veterinarian have decided against treatment at this time, you need to monitor your dog closely for a worsening of symptoms. Keeping a diary is helpful. Jot down how frequently you have to fill your dog’s water bowl, when you need to clean up “accidents” or let your dog out in the middle of the night to urinate, how long your leash walks are, etc. Your dog will also need to be seen by your veterinarian regularly.
Dogs who are taking trilostane or mitotane need to be watched carefully. The goal of treating Cushing’s disease in dogs is to give enough of the medication to reduce the clinical signs to an acceptable level, but not so much that unwanted side effects develop. Expect to return to the veterinary clinic every few weeks during the initial phases of treatment, but once your dog’s condition is stable rechecks usually can be scheduled every 3-6 months.
Standard post-operative care is required after an adrenal tumor has been removed. Restrict your dog’s activity (short leash walks only) for 10-14 days postoperatively and closely follow your veterinarian’s instructions.
Questions to Ask Your Vet
If your dog has been diagnosed with Cushing’s disease while on or soon after stopping any type of medication (oral, injectable, or topical) that contains a corticosteroid (e.g., prednisone or dexamethasone), ask your veterinarian if the medication could be the cause. Cushing’s disease can develop as a result taking corticosteroids. Treatment involves slowly weaning dogs off of the medication.
If your dog’s symptoms don’t seem too bothersome and your veterinarian is recommending treatment, ask why or get a second opinion. Because treating Cushing’s disease in dogs is time consuming, expensive, and potentially dangerous, it is best reserved for moderate to severe cases. The medication selegiline is sometimes prescribed when more aggressive treatment isn’t appropriate, but its effectiveness is questionable.
Possible Complications to Watch For
If you decide against treating your dog’s Cushing’s disease, be aware that he or she is at a somewhat higher risk for developing diabetes mellitus and rupturing a cranial cruciate (knee) ligament.
Dogs on trilostane or mitotane can develop Addison’s disease, a condition associated with underproduction of the hormone cortisol. Symptoms of Addison’s disease in dogs include lethargy, poor appetite, vomiting, diarrhea, and collapse.
If your dog has had surgery to remove an adrenal tumor, watch closely for signs of internal bleeding (weakness, rapid breathing, a swollen belly, and pale gums). Check your dog’s incision several times a day for infection (abnormal redness, swelling, or drainage), missing sutures, and anything else that appears abnormal.
Call your veterinarian immediately if you have any concerns or questions about your dog’s condition.
IMAGE: Patrick Michael McLeod via Flickr
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