Addison's Disease

Addison's disease waxes and wanes, which is why many pets have multiple unexplained illness episodes before a diagnosis is reached. Owners sometimes notice a "waxing and waning" pattern where the dog seems to improve on its own (or with supportive fluids), then deteriorates again weeks later.

• Vomiting and diarrhea — often episodic and without an obvious cause
• Lethargy and weakness, sometimes so profound the dog can't stand
• Loss of appetite and weight loss over weeks to months
• Shaking or shivering, even in warm environments
• Increased thirst and urination (seen in some but not all cases)
• Slow heart rate despite signs of collapse or weakness
• Painful, tense abdomen
• In an Addisonian crisis: sudden collapse, severe weakness, shock, abnormal heart rhythm

The episodic nature and the combination of GI signs with weakness are important clues. A dog that collapses or has a dangerously slow heart rate deserves immediate emergency evaluation.

Most cases of Addison's disease are caused by immune-mediated destruction of the adrenal cortex — the immune system attacks the gland as if it were foreign tissue. Less commonly, Addison's results from:

• Sudden withdrawal from prolonged corticosteroid therapy, which suppresses the adrenal glands' own production
• Mitotane (Lysodren) over-treatment for Cushing's disease, which can destroy too much adrenal tissue
• Trauma, infection, or hemorrhage affecting both adrenal glands (rare)

Risk factors for the immune-mediated form include:

• Breed — Standard Poodles, Bearded Collies, Portuguese Water Dogs, Great Danes, West Highland White Terriers, and Rottweilers are predisposed; genetic testing is available for some breeds
• Sex — females are affected roughly twice as often as males
• Age — peak onset is between two and seven years old, though any age is possible

An Addisonian crisis is often diagnosed partly on the basis of a characteristic blood panel abnormality before the confirmatory test is run. The key findings and tests include:

• Electrolyte abnormalities on the chemistry panel — a low sodium-to-potassium ratio (below 27:1) is a classic and urgent clue pointing to Addison's
• ACTH stimulation test — the definitive test; cortisol is measured before and after an injection of synthetic ACTH; dogs with Addison's show little or no cortisol rise. This test is performed in-house with same-day results
• CBC and chemistry panel — often reveals mild anemia, low blood sugar, elevated kidney values, and the electrolyte imbalance
• Electrocardiogram (ECG) — high potassium can cause dangerous arrhythmias; an ECG helps guide emergency management
• Abdominal imaging — to look for adrenal gland size (typically small in Addison's) and rule out other causes of collapse

An important note: dogs with "atypical" Addison's lack the electrolyte abnormality because only cortisol is deficient, not aldosterone. These dogs can be missed without the ACTH stimulation test.

Treatment has two phases — crisis stabilization and long-term maintenance:

• Emergency stabilization — intravenous fluids (normal saline) to restore sodium and blood pressure, injectable glucocorticoids (dexamethasone or hydrocortisone), and cardiac monitoring until the pet is stable
• Long-term mineralocorticoid replacement — most dogs receive either desoxycorticosterone pivalate (DOCP, a monthly or quarterly injection) or fludrocortisone (daily oral tablet) to replace aldosterone and maintain safe electrolyte levels
• Glucocorticoid supplementation — a low daily dose of prednisone (or hydrocortisone) replaces cortisol; the dose is increased during illness, surgery, or any stressful event — a critical concept called "stress dosing"

Most owners quickly learn to recognize early warning signs and increase the prednisone dose at home during stressful events, preventing crises. Periodic bloodwork (electrolytes every 3–6 months) lets us fine-tune the DOCP dose.

An Addisonian crisis — sudden collapse, profound weakness, or a shaking dog that can't stand — is an emergency. Call us immediately. For non-crisis situations, any dog with repeated vomiting-and-lethargy episodes without a clear cause, especially in a susceptible breed, deserves an ACTH stimulation test — it is the only way to rule out Addison's definitively. Once diagnosed and stabilized on replacement therapy, our Calabasas team manages routine rechecks to keep your dog's electrolytes balanced and their life completely normal. Book an appointment or call us directly for urgent concerns.