Addison’s disease in dogs, medically known as hypoadrenocorticism, is an endocrine disorder that results from inadequate production of critical adrenal hormones. Although the condition is uncommon, it remains clinically important because it can mimic many other illnesses. For this reason, clinicians often call it “the great pretender.” Early recognition and appropriate treatment are essential, since untreated Addison’s disease can become life threatening. With timely diagnosis and lifelong management, however, most affected dogs live normal, high quality lives.
What Is Addison’s Disease?
Addison’s disease develops when the adrenal glands do not produce sufficient hormones from the adrenal cortex. The adrenal cortex contains three distinct layers. The zona glomerulosa produces aldosterone, the zona fasciculata produces cortisol, and the zona reticularis produces androgens.
Cortisol plays a central role in the body’s stress response and regulates blood pressure, glucose metabolism, and immune function. The hypothalamic pituitary adrenal axis controls its secretion. Aldosterone regulates sodium and potassium balance and maintains hydration and blood pressure through renal effects. When hormone levels fall, dogs lose the ability to maintain normal electrolyte balance, blood pressure, and physiologic stress responses.
Types of Hypoadrenocorticism
Primary hypoadrenocorticism represents the most common form. In most cases, immune mediated destruction eliminates more than 90% of the adrenal cortex. Less commonly, neoplasia or infectious and inflammatory diseases damage both adrenal glands.
Secondary hypoadrenocorticism develops when the pituitary gland does not produce adequate adrenocorticotropic hormone, often after chronic glucocorticoid administration. In this form, cortisol decreases, but aldosterone production usually remains intact.
Atypical hypoadrenocorticism, also known as eunatremic eukalemic Addison’s disease, causes cortisol deficiency without sodium or potassium abnormalities. No single laboratory variable reliably excludes this form, which underscores the importance of cortisol testing in suspicious cases.
Which Dogs Are at Risk?
Addison’s disease most often affects young to middle aged dogs and occurs more frequently in females. Certain breeds show increased risk, including Standard Poodles, Wheaten Terriers, Portuguese Water Dogs, and West Highland White Terriers. Cats rarely develop this condition.
Clinical Signs: Why Addison’s Is Often Missed
Hypoadrenocorticism does not produce a pathognomonic presentation. Clinical signs may appear acutely and severely or develop chronically with intermittent episodes. Because the signs overlap with many gastrointestinal, renal, and metabolic disorders, clinicians frequently overlook the disease.
Common signs include weakness, lethargy, vomiting, diarrhea, decreased appetite, weight loss, dehydration, and increased thirst or urination. Some dogs experience waxing and waning gastrointestinal signs for weeks or months before veterinarians establish a diagnosis.
In severe cases, dogs present in Addisonian crisis with hypovolemic shock. These patients may exhibit profound weakness, collapse, hypotension, pale mucous membranes, hypothermia, and cardiac arrhythmias secondary to hyperkalemia. Electrocardiography may reveal bradycardia, tented T waves, absent P waves, and prolonged PR intervals.
Less common manifestations also occur. Some dogs develop megaesophagus, hypoglycemic seizures, or reversible ventricular dilation with systolic dysfunction. Clinicians should therefore include hypoadrenocorticism on the differential list when dogs present with unexplained shock, electrolyte abnormalities, or atypical cardiac findings.
Diagnostic Approach
A thorough history and physical examination provide the foundation for diagnosis, but laboratory testing often raises the first suspicion. A minimum database frequently reveals characteristic abnormalities. On complete blood count, dogs often lack a stress leukogram and instead show normal or increased lymphocytes or eosinophils. On serum biochemical profile, clinicians commonly identify hyponatremia, hyperkalemia, a low sodium to potassium ratio, azotemia, hypoalbuminemia, hypoglycemia, hypocholesterolemia, and occasionally hypercalcemia. Urinalysis often shows inappropriately dilute urine.
Measurement of a resting basal cortisol concentration serves as a practical screening test. A basal cortisol concentration greater than 2 ug/dL effectively excludes Addison’s disease in most dogs not receiving corticosteroids. Values below 2 ug/dL require confirmatory testing.
The ACTH stimulation test remains the gold standard for diagnosis. Clinicians collect a baseline cortisol sample, administer synthetic ACTH intravenously at 1 ug/kg, and measure cortisol again one hour later. Dogs with hypoadrenocorticism fail to mount an appropriate cortisol response, and both pre and post ACTH cortisol concentrations remain low. Although researchers have investigated alternative strategies such as endogenous ACTH measurement and urine cortisol:creatinine ratios, the ACTH stimulation test remains the most reliable confirmatory method.
Treatment of Addison’s Disease
Treatment depends on clinical presentation.
Dogs in Addisonian crisis require immediate stabilization. Clinicians administer aggressive intravenous fluids to restore circulating volume, give calcium gluconate for cardioprotection when potassium exceeds 6.5 mmol/L, and use dextrose with or without regular insulin to reduce hyperkalemia. They initiate glucocorticoid supplementation promptly with dexamethasone. Once cardiovascular stability returns and the patient resumes eating and drinking, clinicians transition to oral prednisone.
Long term management requires lifelong glucocorticoid supplementation at physiologic doses, with temporary dose increases during stress or illness. Dogs with typical Addison’s disease also need mineralocorticoid replacement. Clinicians commonly administer desoxycorticosterone pivalate injections every 25 to 30 days, and evidence supports lower starting doses in many patients. Alternatively, they may prescribe oral fludrocortisone; approximately half of treated dogs do not require additional glucocorticoid supplementation.
Clinicians must monitor electrolytes and clinical signs regularly. They should also reassess dogs with atypical Addison’s disease periodically, because some later develop electrolyte abnormalities that require mineralocorticoid therapy.
Prognosis
Dogs that survive an initial Addisonian crisis carry an excellent prognosis. With consistent medication, routine monitoring, and appropriate stress dosing, most dogs live normal lives. Although the diagnosis requires lifelong management, the long term outlook remains highly favorable.
Key Takeaway
Addison’s disease in dogs is an adrenal disorder characterized by insufficient cortisol production and, in many cases, inadequate aldosterone production. Because clinical signs often appear vague and nonspecific, clinicians must maintain a high index of suspicion. With appropriate diagnostic testing and lifelong hormone replacement, affected dogs can thrive.nal signs, electrolyte abnormalities, or shock that does not fit typical patterns, hypoadrenocorticism should remain on the differential list.
