Addison's disease (hypoadrenocorticism) is the opposite of Cushing's — the adrenal glands produce insufficient cortisol and aldosterone. It's called "the great pretender" because its vague, waxing-and-waning symptoms mimic dozens of other conditions. Dogs are often misdiagnosed for months before an Addisonian crisis reveals the true diagnosis — sometimes nearly fatally.
What Happens
The adrenal glands produce two critical hormone groups:
- Glucocorticoids (cortisol): Stress response, metabolism, immune regulation, blood sugar maintenance
- Mineralocorticoids (aldosterone): Sodium/potassium balance, blood pressure, fluid regulation
Without these hormones, the body cannot respond to stress, maintain electrolyte balance, or regulate blood pressure. Minor stresses that healthy dogs handle easily (vet visits, boarding, dietary changes) can trigger life-threatening collapse in Addisonian dogs.
Symptoms
- Waxing and waning lethargy (good days and bad days)
- Intermittent vomiting and/or diarrhea
- Decreased appetite (comes and goes)
- Weight loss
- Muscle weakness
- Shaking/trembling
- Increased thirst and urination (less common than Cushing's)
The pattern: Symptoms that come and go, often worsening during stressful events, then partially resolving on their own. This episodic nature leads to misdiagnosis as "sensitive stomach," "anxiety," or "just getting older."
Addisonian Crisis (Emergency)
- Collapse/shock
- Severe dehydration
- Bradycardia (slow heart rate — a key diagnostic clue)
- Vomiting/diarrhea
- Hypothermia
- Dangerously elevated potassium (causes fatal cardiac arrhythmias)
Treatment: aggressive IV fluid resuscitation, dexamethasone, correction of electrolyte abnormalities. Most dogs respond dramatically within hours with appropriate emergency treatment.
Diagnosis
- Electrolytes: Classic finding — low sodium, high potassium (Na:K ratio <27:1). But 30% of Addisonian dogs have normal electrolytes ("atypical Addison's").
- ACTH stimulation test: The definitive diagnostic test. Measures cortisol before and after synthetic ACTH injection. Addisonian dogs show minimal to no cortisol response.
- Baseline cortisol: A resting cortisol >2 μg/dL essentially rules OUT Addison's (useful screening test).
Treatment
| Medication | Replaces | Route | Frequency | Cost |
|---|---|---|---|---|
| DOCP (Percorten-V/Zycortal) | Mineralocorticoid (aldosterone) | Injection | Every 25-28 days | $50-$150/injection |
| Fludrocortisone (Florinef) | Mineralocorticoid | Oral (daily) | Twice daily | $30-$100/month |
| Prednisone | Glucocorticoid (cortisol) | Oral | Daily (low dose) | $5-$15/month |
Stress dosing: During known stressful events (vet visits, travel, surgery, illness), prednisone dose is temporarily increased 2-5x to replace the cortisol surge that healthy dogs produce naturally.
Prognosis
Excellent with proper treatment. Addisonian dogs on appropriate replacement therapy live normal lifespans with normal quality of life. The disease is manageable but requires lifelong medication and owner awareness of stress management.
Frequently Asked Questions
Which breeds get Addison's?
Standard Poodles, Portuguese Water Dogs, Bearded Collies, West Highland White Terriers, Great Danes, and Nova Scotia Duck Tolling Retrievers have genetic predispositions. Young to middle-aged females are most commonly affected.
