Updates on hypoadrenocorticism

The lack of a stress leukogram in dogs with gastrointestinal signs may signal this potentially life-threatening disease. This review will help ensure that you aren't overlooking other clinical signs and that you know the latest about diagnosing and treating canine hypoadrenocorticism.
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Jun 01, 2008

Hypoadrenocorticism may be difficult to recognize because of its varied clinical presentation. Furthermore, it may not be first on your differential diagnosis list because it is a relatively uncommon endocrine disease in dogs. However, it is important to be able to quickly identify this disease since prompt diagnosis and treatment can result in an excellent long-term prognosis. To help you better recognize and treat affected patients, this review discusses the etiology, diagnosis, and treatment of the different types of hypoadrenocorticism in dogs.

TYPES OF HYPOADRENOCORTICISM


Photo by Mark McDonald
In the adrenal cortex, glucocorticoids are produced in the zona fasciculata and zona reticularis, and mineralocorticoids are produced in the zona glomerulosa. Glucocorticoid production is stimulated by ACTH from the pituitary gland. Mineralocorticoids, on the other hand, are released in response to either hypovolemia, which triggers the renin-angiotensin system, or hyperkalemia, which directly stimulates adrenocortical tissue.1,2

Hypoadrenocorticism, also known as Addison's disease, is caused by either destruction of the adrenal cortex (primary hypoadrenocorticism) or a lack of ACTH release from the pituitary gland (secondary hypoadrenocorticism).3 Primary hypoadrenocorticism may result in a deficiency of glucocorticoids, mineralocorticoids, or both.1-3 In our experience, some dogs that initially have primary glucocorticoid deficiency (i.e. adrenal dysfunction) alone will eventually develop mineralocorticoid deficiency, but there are reports of dogs with primary glucocorticoid deficiency having clinically adequate mineralocorticoid production for years after initial diagnosis.4-7 Secondary hypoadrenocorticism (i.e. pituitary dysfunction) results in glucocorticoid deficiency only. The mineralocorticoids are spared since ACTH has limited effect on the zona glomerulosa.3 Mineralocorticoid deficiency without concurrent glucocorticoid deficiency is rare in dogs.3

CAUSES

Immune-mediated destruction of the adrenal cortex is the most common cause of primary hypoadrenocorticism.2,3 Other less common causes include neoplasia, thromboembolism, and granulomatous disease.2 Secondary hypoadrenocorticism may develop from pituitary damage due to neoplasia, inflammation, or trauma.2,5,8 Iatrogenic hypoadrenocorticism may result from the administration of adrenocorticolytic drugs such as mitotane or long-term glucocorticoid therapy.9

SIGNALMENT

Hypoadrenocorticism is most often diagnosed in young to middle-aged female dogs but has been recognized in both male and female dogs between 4 months and 14 years of age.6,8 Standard poodles, Portuguese water dogs, Great Danes, rottweilers, West Highland white terriers, and Wheaton terriers are some of the overrepresented breeds.8,10 Hypoadrenocorticism may be inherited in certain breeds, such as Portuguese water dogs, and a complete genetic evaluation of hypoadrenocorticism is being investigated in many breeds.10