What is Addison's disease in dogs?

Hypoadrenocorticism is the failure of the adrenal glands to produce glucocorticoids (cortisol) and/or mineralocorticoids (aldosterone). Without these hormones the body cannot regulate metabolism or electrolyte balance.

What are the symptoms of Addison's disease in dogs?

Episodic weakness, lethargy, vomiting, diarrhoea, weight loss, anorexia, tremors and muscle wasting. Symptoms are non-specific and episodic, making diagnosis notoriously difficult (hence "the great imitator").

What is an Addisonian crisis?

An acute medical emergency in which cortisol and aldosterone collapse suddenly. The dog shows severe hypoglycaemia, hypotension, bradyarrhythmias from hyperkalaemia, extreme collapse and can die within hours without treatment.

How is Addison's disease treated in dogs?

Lifelong hormone replacement: oral fludrocortisone or monthly DOCP (desoxycorticosterone pivalate/Zycortal) injections for mineralocorticoids, plus low-dose prednisolone for glucocorticoids. With treatment, dogs have an excellent quality of life.

Addison's Disease in Dogs: Symptoms, Crisis and Treatment

What Is Hypoadrenocorticism?

The adrenal cortex produces vital hormones: glucocorticoids (cortisol) regulate metabolism, the stress response and the immune system; mineralocorticoids (aldosterone) control the balance of sodium, potassium and water. In Addison's disease, the adrenal cortex fails — typically through immune-mediated destruction — and both hormones become deficient.

Why "The Great Imitator"?

Symptoms are vague, non-specific and episodic: the dog may be perfectly well between episodes, then present with weakness, vomiting and lethargy that improve spontaneously or with symptomatic treatment. As a result, dogs often go months or years without the correct diagnosis, being treated for gastroenteritis, liver disease or other conditions.

Symptoms

Recurrent episodes of weakness, lethargy and collapse.
Vomiting and diarrhoea — sometimes with blood.
Weight loss and muscle wasting.
Anorexia or variable appetite.
Muscle tremors.
Polyuria/polydipsia in some cases.
Addisonian crisis: sudden collapse, hypothermia, bradycardia from hyperkalaemia, shock — a life-threatening emergency.

Predisposed Breeds

Portuguese Water Dog, Bearded Collie, Standard Poodle, Nova Scotia Duck Tolling Retriever, Labrador Retriever, Leonberger, West Highland White Terrier and Rottweiler. Also Golden Retriever and Wheaten Terrier. More common in females and young to middle-aged dogs (4-7 years), though it can occur at any age.

Diagnosis

ACTH stimulation test: the definitive test — basal and post-ACTH cortisol <2 μg/dL confirms hypoadrenocorticism.
Biochemistry and electrolytes: hyperkalaemia, hyponatraemia, hypoglycaemia, pre-renal azotaemia.
ECG: bradycardia and T-wave changes from hyperkalaemia.

Treatment

Addisonian crisis (emergency):

IV fluids: 0.9 % saline at shock dose to correct hyperkalaemia and hypotension.
Dexamethasone IV (does not interfere with the ACTH test).
IV glucose if hypoglycaemic.

Long-term maintenance:

DOCP (desoxycorticosterone pivalate): IM/SC injection every 25-28 days — replaces mineralocorticoids.
Oral fludrocortisone: alternative that covers both mineralocorticoids and glucocorticoids.
Oral prednisolone: physiological low dose (0.1-0.2 mg/kg/day), increased ×3 during stress (travel, vet visits).

With appropriate treatment, dogs with Addison's have a normal life expectancy and an excellent quality of life.