Cushing’s syndrome in dogs occurs when function of the adrenal glands are hyper-stimulated and begin to produce too much of a hormone, causing a massive instability in the endocrine system. Cushing’s disease is the exact opposite of Addison’s disease.
Signs & Symptoms of Cushing’s Syndrome
- Increase in appetite
- Low energy; lethargy
- Drinking and urinating a lot (polydipsia/polyuria)
- “Pot bellied” appearance is commonly noted (Due to the increased layer of fat around the abdomen walls and organs, the abdomen becomes heavy and hangs down)
Causes of Cushing’s Syndrome
The adrenal glands are located next to the kidneys and their job is to produce hormones which are responsible for regulating the fight or flight response, and hormones that are responsible for keeping electrolytes, such as potassium and sodium, balanced. Hyperadrenocorticism is the medical term for Cushing’s syndrome.
hyper – high + adreno – adrenal gland + cortico – cortisol
Cortisol is a steroid which is produced from the adrenal gland and is involved in stress regulation. Aldosterone is the other hormone produced from these glands, and is involved in the balance of electrolytes. When there is an increase in production of these two hormones, cortisol and aldosterone, this is referred to as Cushing’s syndrome.
Cushing’s syndrome can be linked to three different reasons as to why it occurs. It is important to note that, regardless of the cause, the clinical signs are essentially the same, but the treatments, as well as the prognosis, are very different.
Pituitary gland tumor - The leading cause of Cushing’s syndrome in dogs is a tumor of the pituitary gland. Over half of the cases diagnosed are due to pituitary gland tumors. The tumor causes the pituitary to overproduce and stimulates the adrenal glands to produce more cortisol than is necessary. With a pituitary gland tumor, if the activity of the adrenal gland can be controlled, the prognosis can be favorable. A large percentage of dogs with this kind of Cushing’s disease can live a long and relatively normal life as long as medication is given as prescribed and follow-up visits are done with the veterinarian. If the tumor begins to grow, the prognosis becomes less favorable.
Adrenal gland tumor - If a tumor is found on the adrenal gland, further diagnosis must be done to determine if it is benign or malignant. If benign, surgical removal simply cures the disease. If malignant, surgery may help for a while, but the prognosis becomes guarded.
Iatrogenic - Iatrogenic Cushing’s syndrome in dogs means that the excess of cortisol has resulted from excessive administration of a steroid. Basically, if your dog has been on oral steroids or injectable steroids over a long period, then Cushing’s syndrome can be the result.
Diagnosis of Cushing’s Syndrome
Diagnosis begins with a complete history and a physical exam. Your veterinarian will most likely do the following:
- ACTH stimulation test - This will test the adrenal glands function and is the key test when making this diagnosis. The ACTH hormone travels from the pituitary gland through the blood and triggers the adrenal glands to produce cortisol, which is important in many bodily functions. A healthy dog will have heightened levels of cortisol after the injection. Your veterinarian will take a blood sample before and after an injection of synthetic ACTH to measure the level of cortisol produced. This will require a day stay in the hospital for your dog.
- Low-Dose Dexamethasone Suppression test (LDDS) - This test involves an initial baseline blood sample, an injection of the steroid Dexamethsone, and two subsequent blood draws 4 and 8 hours later. Dexamethasone will suppress the amount of cortisol in a healthy dog, and the cortisol levels will be less than the level before the injection. In a dog with Cushing’s syndrome, the levels will be elevated due to an excessive amount of cortisol being produced. This will require a day stay in the hospital for your dog.
- Urinalysis - This test involves collecting a urine sample. If your dog is blocked or will not urinate over time, your veterinarian may have to obtain the sample via cystocentesis, or by putting a needle through the abdomen into the bladder. The urine will then be examined visually, chemically, and microscopically for abnormalities. Your veterinarian will look for red blood cells, crystal formation within the bladder, and abnormal pH or chemical values in the urine.
- Radiographs - This will show a distended abdomen with a thick layer of fat around the abdominal wall and organs.
- Ultrasound - This will show a distended abdomen with a thick layer of fat around the abdominal wall and organs.
Treatment for Cushing’s Syndrome
Iatrogenic Cushing’s Disease
Treatment begins with the termination of the steroid that is being given to your dog. This is done under the direction of your veterinarian and must be done in a controlled manner so that other complications do not occur.
Adrenal Gland Tumor
Treatment of an adrenal gland tumor normally requires major abdominal surgery to attempt to remove the tumor that is causing the problem. In cases where surgery is not an option, there are specific medications that can be used to help manage the syndrome.
Pituitary Gland Tumor
Treatment of the pituitary gland tumor is the most complex. There are two drugs commonly used to treat this version of Cushing’s syndrome. One drug is given daily and usually for the life of your dog. The other drug treatment requires very close monitoring from you and your veterinarian in order to be successful. Both drug therapies involve return visits to your veterinarian for follow-up blood tests and dosing changes. The good news is that with these treatment options, most dogs live a relatively normal life.