Addison's disease is called "the great imitator" because it presents with vague signs—lethargy, vomiting, diarrhea, weight loss—that mimic gastroenteritis, renal disease, and other conditions. The classic electrolyte pattern (hyperkalemia, hyponatremia, hypochloremia) is highly suggestive. Use the Internal Medicine Specialist and Bloodwork OCR for workup guidance.
Primary hypoadrenocorticism results from immune-mediated destruction of the adrenal cortex, leading to deficiency of both glucocorticoids (cortisol) and mineralocorticoids (aldosterone). Aldosterone deficiency causes renal sodium wasting and potassium retention—hence hyperkalemia and hyponatremia.
Secondary Addison's (pituitary disease) causes only glucocorticoid deficiency; electrolytes are usually normal. Breeds at risk: Standard Poodles, Portuguese Water Dogs, West Highland White Terriers.
Baseline cortisol <2 mcg/dL is highly suggestive; ACTH stimulation test confirms. Post-ACTH cortisol fails to rise in Addison's. Electrolytes: Na:K ratio <27 supports diagnosis. ECG may show bradycardia, spiked T-waves from hyperkalemia.
Warning: Addisonian crisis is life-threatening. Dogs present in shock (hypotension, bradycardia, weakness). Immediate treatment: IV fluids (0.9% NaCl), dexamethasone (0.5-2 mg/kg IV), and electrolyte monitoring. Do not delay for ACTH test—treat first.
Mineralocorticoid replacement: fludrocortisone acetate (Florinef) 0.01-0.02 mg/kg PO daily, or desoxycorticosterone pivalate (DOCP) injection every 25-30 days. Glucocorticoid: prednisone 0.2-0.4 mg/kg daily (lower for maintenance, increase during stress).
Stress dosing: double or triple prednisone during illness, surgery, or travel. Owners should always have extra prednisone and know when to increase. Missing doses can precipitate crisis.
- Addison's presents with vague GI signs; Na:K <27 is classic.
- ACTH stimulation test confirms; baseline cortisol <2 mcg/dL suggestive.
- Crisis: IV fluids, dexamethasone, treat before full workup.
- Long-term: fludrocortisone or DOCP + prednisone; stress dosing critical.
- Never stop glucocorticoids abruptly.