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Formally known as hyperadrenocorticism, Cushing's disease is an adrenal disease with three potential causes: pituitary gland tumors, adrenal gland tumors and too much cortisol from extensive steroid use. Care and treatment of a dog with Cushing's disease depends on the cause and may include medication or surgery.
The Endocrine System and Cushing's Disease
Your dog's pituitary gland, at the base of his brain, and his adrenal glands, situated at his kidneys, are part of his endocrine system that delivers hormones throughout his body. These two glands work together to produce corticosteroids. The pituitary gland produces Adrenocorticotropic hormone, or ACTH, that in turn stimulates the adrenal glands to make cortisol. When one of these glands isn't functioning properly, resulting in too much cortisol, many of his bodily functions may be impacted, resulting in a variety of symptoms. Common symptoms of Cushing's disease include increased water consumption, urination and appetite, as well as hair loss on the body, lethargy, weight gain and increased skin, ear and urinary tract infections. Often, dogs have a bloated appearance due to the increased fat in the abdominal organs and stretching of the abdominal wall from heavier organs.
Pituitary-Dependent Cushing's Disease
According to VCA Animal Hospitals, pituitary gland tumors are the most common cause of Cushing's disease in dogs, responsible for approximately 85 to 90 percent of all cases. The tumor, which may be malignant or benign, large or tiny, causes the pituitary gland to make too much ACTH, causing the adrenal glands to make too much cortisol. If your dog has been diagnosed with pituitary-dependent Cushing's disease, he'll need to take medication the rest of his life. Typically, trilostane and mitotane are the medications used to regulate the amount of ACTH produced by the pituitary gland. The dog usually goes through an induction phase, when he's given mitotane once or twice a day for approximately a week. After the induction phase, the dosage is decreased to once or twice a week for the balance of the dog's life. Trilostane requires daily administration.
Mitotane has side effects that include vomiting, diarrhea, appetite loss, depression and incoordination, often a result of a quick or excessive drop in cortisol level. Trilostane may have similar effects, though they tend to be more mild. The vet may prescribe other medication to use in an emergency situation if the cortisol level decreases too much, too fast from mitotane.
Adrenal-Dependent Cushing's Disease
Adrenal tumors are responsible for causing approximately 15 percent of the cases of Cushing's disease in dogs. Whether malignant or benign, surgery is the treatment of choice for this type of hyperadrenocorticism. The prognosis depends on the tumor itself; if benign, removal will cure the disease and the dog likely will have a favorable outcome. If the tumor is malignant, the surgery may buy the dog some time, however, the prognosis is less favorable. Medication may help a dog with adrenal-dependent Cushing's disease if surgery is not recommended, given the size or location of the tumor or the dog's health.
Iatrogenic Cushing's Disease
If your dog has a condition requiring long-term use of steroids, it's possible his Cushing's disease developed from their use. Known as iatrogenic Cushing's disease, the vet gradually will discontinue the steroid to avoid potential complications. Additional treatment will depend on the original condition the steroid addressed and also may require hormone replacement to supplement the hormones lost from the impaired adrenal gland function.
Follow Doctor's Orders
If your dog's Cushing's disease is pituitary-dependent, his prognosis is generally favorable, however it's up to you to ensure he takes his medicine as directed by the vet. Your vet will instruct you on what side effects to look for as well as when to take your dog for follow-up checkups and blood tests. Blood work will ensure your dog is taking the proper amount of medication.