Cushing's Disease in Dogs: A Guide to this Hormonal Disorder

A guide to Cushing's Disease (Hyperadrenocorticism) in dogs. Learn how the overproduction of cortisol causes signs like a pot-belly and hair loss, and understand the complex diagnostic process and treatment options.

Hey there, pet parents. Today we're going to talk about another common hormonal disease in older dogs, one that can be a bit of a master of disguise: Cushing's Disease. The official name is Hyperadrenocorticism, which is a mouthful, so we'll stick with Cushing's. It's a condition caused by the overproduction of the body's natural steroid, cortisol.

What is Cushing's Disease?

Cortisol is a stress hormone produced by the adrenal glands (two small glands that sit on top of the kidneys). It's vital for life and helps the body respond to stress. However, when the body produces too much cortisol over a long period of time, it can be very damaging.

There are two main causes of Cushing's disease:

  1. •Pituitary-Dependent Cushing's (PDH): This is the most common cause, accounting for about 85% of cases. It's caused by a tiny, benign tumor in the pituitary gland at the base of the brain. This tumor produces too much of a hormone called ACTH, which in turn tells the adrenal glands to produce way too much cortisol.
  2. 1Adrenal-Dependent Cushing's (ADH): This form is caused by a tumor on one of the adrenal glands itself, which secretes excess cortisol. About half of these tumors are benign, and half are malignant.

There is also a third type, called Iatrogenic Cushing's, which is caused by the long-term use of high-dose steroid medications (like prednisone) for other conditions like allergies.

Spotting the Signs of Cushing's

The signs of Cushing's disease are often mistaken for normal signs of aging, as they come on very gradually.

  • •Increased Thirst and Urination (Polydipsia/Polyuria): This is one of the most common signs. The dog is drinking and urinating excessively.
  • •Increased Appetite (Polyphagia): They are ravenously hungry all the time.
  • •A "Pot-Bellied" Appearance: The high cortisol levels weaken the abdominal muscles, causing the belly to sag.
  • •Muscle Wasting: You might notice muscle loss, especially over the back and shoulders.
  • •Skin and Coat Problems:
    • •Symmetric hair loss on the body (sparing the head and legs).
    • •Thin, fragile skin.
    • •Recurrent skin infections.
    • •Hard, gritty bumps in the skin called calcinosis cutis.
  • •Excessive Panting: Even when at rest.
  • •Lethargy: Decreased energy and activity.

The Challenge of Diagnosis

Diagnosing Cushing's disease can be tricky. There is no single, perfect test for it. Your vet will use a combination of your dog's clinical signs, routine bloodwork, and specific hormonal tests.

  • •Routine Bloodwork: Will often show some classic clues, like a high level of an enzyme called ALP (alkaline phosphatase).
  • •Urine Test (Urine Cortisol:Creatinine Ratio): This is a good screening test. If the result is normal, it's very unlikely the dog has Cushing's. If it's high, it could be Cushing's, but it could also be due to another illness (as any stress can raise cortisol).
  • •Specific Endocrine Tests: If Cushing's is suspected, your vet will need to perform a specific hormonal test to confirm it. The two most common are:
    1. •Low-Dose Dexamethasone Suppression (LDDS) Test: This is the test of choice for many vets. It involves taking a baseline blood sample, giving an injection of a steroid (dexamethasone), and then taking two more blood samples over an 8-hour period. In a normal dog, the dexamethasone should suppress cortisol production. In a Cushingoid dog, it doesn't.
    2. •ACTH Stimulation Test: This test involves taking a baseline blood sample, giving an injection of ACTH (the hormone that stimulates the adrenal glands), and then taking another blood sample an hour later. In a Cushingoid dog, the adrenal glands will over-react and produce a very high level of cortisol.

Once the diagnosis is confirmed, an abdominal ultrasound is often performed to look at the adrenal glands. This helps to differentiate between the pituitary-dependent and adrenal-dependent forms of the disease.

Treatment Options

The goal of treatment is to reduce the amount of cortisol in the body to a safe level, which will resolve the clinical signs and improve the dog's quality of life.

  • •

    For Pituitary-Dependent Cushing's (PDH): The treatment of choice is medical management.

    • •Trilostane (Vetoryl): This is the most common medication used today. It works by inhibiting an enzyme that is needed to produce cortisol. It's given as a daily pill. Dogs on Trilostane need to be monitored very carefully with regular bloodwork and ACTH stimulation tests to make sure the cortisol level doesn't go too low.
    • •Mitotane (Lysodren): This is an older medication that works by selectively destroying the cortisol-producing cells of the adrenal gland. It's less commonly used now due to a higher risk of side effects.
  • •

    For Adrenal-Dependent Cushing's (ADH): If the adrenal tumor has not spread, the treatment of choice is surgery to remove the affected adrenal gland. This is a specialized surgery. If surgery is not an option, medical management with Trilostane can be used.

Prognosis

Cushing's disease is a serious condition, but with successful treatment, the clinical signs can be well-managed, and dogs can have a good quality of life for several years. The key is careful, lifelong monitoring with your veterinarian.

Sources & Further Reading:

  1. •VCA Animal Hospitals - Cushing's Disease in Dogs
  2. 1American Kennel Club - Cushing's Disease in Dogs