Hypoadrenocorticism in dogs
Hypoadrenocorticism in dogs, or, as it is known in people, Addison's disease, is an endocrine system disorder that occurs when the adrenal glands fail to produce enough hormones for normal function.
The adrenal glands secrete glucocorticoids such as cortisol[1] and mineralocorticoids such as aldosterone;[2] when proper amounts of these are not produced, the metabolic and electrolyte balance is upset.
The usual causes are genetic, often related to autoimmune disorders, where the body attacks and kill its own tissue ("immune mediated destruction").
[8] Other cases are caused by various disease processes,[8][9][10] including failure of the pituitary gland to secrete ACTH, the hormone which stimulates the adrenal production of cortisol.
[9][11] The most common clinical manifestations are related to mental status and gastrointestinal function; they include lethargy, anorexia, vomiting, weight loss, and weakness.
Bilateral destruction of the adrenal cortex by neoplasia (e.g. lymphosarcoma), granulomatous disease, or arterial thrombosis can also cause primary adrenocortical insufficiency.
Destructive lesions (e.g. neoplasia, inflammation) in the pituitary gland or hypothalamus and chronic administration of exogenous glucocorticoids or megestrol acetate (cats) are the most common causes.
[13] The usual protocol for stopping steroid medications is not to eliminate them suddenly, but to withdraw from them gradually in a "tapering off" process, which allows the production to adjust to normal.
[13] Hypoadrenocorticism is often tentatively diagnosed on the basis of history, physical findings, clinical pathology, and, for primary adrenal insufficiency, characteristic electrolyte abnormalities.
[20] The ACTH stimulation test does not distinguish between primary and secondary hypoadrenocorticism, or adrenocortical destruction caused by mitotane overdose.
[24] In general, hypoadrenocorticism is underdiagnosed in dogs,[citation needed] and one must have a clinical suspicion of it as an underlying disorder for many presenting complaints.
[26] If deterioration of the adrenal glands progresses far enough, a dog may experience an Addisonian crisis, an acute episode during which potassium levels increase (hyperkalemia), disrupting normal functions of the heart.
[27] Arrhythmia can result and blood pressure may drop to dangerously low levels, while the dog's kidneys may cease to function properly.
[13][27] Breeds that began in the Pacific Rim, among them Akitas and Shiba Inus, tend to have higher potassium values in laboratory test, and elevated levels are not abnormal.
[14][17] Treatment is directed towards (1) correcting hypotension, hypovolemia, electrolyte imbalances, and metabolic acidosis; (2) improving vascular integrity, and (3) providing an immediate source of glucocorticoids.
Over the ensuing 2 to 4 days, a gradual transition from IV fluids to oral water and food is undertaken, and maintenance mineralocorticoid and glucocorticoid therapy is initiated.
Hypoadrenocorticism is typically a disease of young to middle-aged female dogs, although Standard Poodles and Bearded Collies of both sexes are prone to the condition.
