Canine Hypoadrenocorticism (Addison's Disease): NAVLE Study Guide

Addison's is called "the great pretender" for a reason. It walks in looking like gastroenteritis, kidney disease, or just a sick dog that needs fluids. It feels better in the hospital, goes home, and comes back worse two weeks later. The NAVLE loves this condition because it punishes the test-taker who pattern-matches to the most obvious diagnosis without thinking through the whole picture.

Three numbers run this case: the Na:K ratio, the post-ACTH cortisol, and the heart rate. Get those three right and you'll nail every Addison's question on the board.

Why the Adrenal Cortex Fails

Primary hypoadrenocorticism means the adrenal cortex itself is destroyed — immune-mediated adrenalitis accounts for over 90% of cases. All three cortical zones go down: glomerulosa, fasciculata, reticularis. That means you lose both aldosterone and cortisol simultaneously. Secondary hypoadrenocorticism, by contrast, comes from inadequate ACTH from the pituitary. The zona glomerulosa is spared because aldosterone is regulated by the RAAS, not ACTH — so electrolytes stay normal in secondary disease.