Addison's Disease in Dogs: A Guide to the "Great Pretender"

A guide to Addison's Disease (Hypoadrenocorticism) in dogs. Learn why this "Great Pretender" is so tricky to diagnose, the signs of an Addisonian crisis, and how it can be successfully managed with lifelong medication.

Hey, pet parents. We've talked about Cushing's disease, which is the overproduction of cortisol. Now let's talk about its polar opposite: Addison's Disease. The official name is Hypoadrenocorticism, and it's a deficiency of the hormones produced by the adrenal glands. Addison's is known as "The Great Pretender" because its signs can be vague and mimic many other illnesses, making it tricky to diagnose.

What is Addison's Disease?

The adrenal glands produce two main types of hormones:

  1. •Glucocorticoids (mainly cortisol): The "stress" hormone.
  2. 1Mineralocorticoids (mainly aldosterone): This hormone's job is to regulate the body's electrolytes (sodium and potassium) and water balance.

In a dog with typical Addison's disease, the adrenal glands are destroyed (usually by the dog's own immune system) and they can no longer produce either cortisol or aldosterone.

The lack of cortisol makes it hard for the dog to handle stress. The lack of aldosterone is what is truly life-threatening. Without it, the body can't hold onto sodium, and the potassium level in the blood rises to dangerously high levels, which can cause the heart to stop.

There is also an "atypical" form of Addison's where only cortisol is deficient.

Spotting the Signs of Addison's

This is the tricky part. The signs of Addison's are often vague, they come and go, and they can look like many other things.

  • •"Ain't Doin' Right": This is the classic description. The dog is just not well.
  • •Lethargy and Weakness: They just have no energy.
  • •Waxing and Waning GI Upset: Intermittent vomiting, diarrhea, and a poor appetite. The dog seems to get sick, then gets better, then gets sick again.
  • •Weight Loss.
  • •Shaking or Trembling.

Because the signs are so non-specific, a diagnosis is often missed until the dog has an Addisonian Crisis.

The Addisonian Crisis: A Medical Emergency

An Addisonian crisis is a state of acute shock brought on by a stressful event (like boarding or a vet visit) in an undiagnosed Addisonian dog. The signs are:

  • •Sudden, severe weakness and collapse.
  • •Severe vomiting and diarrhea.
  • •A very slow heart rate (bradycardia) due to the high potassium level.
  • •Shock and death if not treated immediately.

An Addisonian crisis is a true, life-threatening emergency that requires immediate, aggressive hospitalization.

How Vets Diagnose Addison's

  • •Routine Bloodwork: In a dog having a crisis, the bloodwork will show some classic clues: a very high potassium and a low sodium. The kidney values will also often be very high, making it look like kidney failure. One of the key clues is that in a very sick, dehydrated dog, a certain type of white blood cell (the neutrophil) should be very high, but in an Addisonian dog, it's often normal. This lack of a "stress response" is a red flag.
  • •The Gold Standard: The ACTH Stimulation Test: This is the same test used to help diagnose Cushing's, but we are looking for the opposite result. A baseline blood sample is taken, the dog is given an injection of ACTH, and another sample is taken an hour later.
    • •In a normal dog, the ACTH will cause the cortisol level to rise significantly.
    • •In an Addisonian dog, the adrenal glands are destroyed and can't produce any cortisol, so the cortisol level will be very low and will not rise at all after the ACTH injection. A "flat-line" ACTH stim test is a definitive diagnosis for Addison's.

Treatment: Replacing the Hormones

The great news is that Addison's disease is very treatable! We just have to replace the hormones that the body is no longer making.

  • •For an Addisonian Crisis: This requires intensive hospitalization with IV fluids to correct the dehydration and electrolyte imbalances, and injections of steroids.
  • •For Long-Term Management:
    1. •Mineralocorticoid Replacement: This is the most important part. It is replaced with either:
      • •Percorten-V (DOCP): An injection that is given by your vet approximately every 25-30 days.
      • •Fludrocortisone: A daily pill.
    2. •Glucocorticoid Replacement: A daily, low dose of a steroid like prednisone is given to replace the missing cortisol. The dose may need to be increased during times of stress.

That's it. Dogs with Addison's need lifelong medication and regular monitoring of their electrolytes, but they can live a completely normal, active life. The key is getting to a diagnosis before they have a life-threatening crisis.

Sources & Further Reading:

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