Hypoadrenocorticism (HOAC;
Addison's disease) is an endocrine condition seen in small animal practice. Dogs with this disease can present in a variety of ways from acute
hypovolemic collapse to vague, chronic, waxing, and waning clinical signs. In the most common form of this disease, animals have both
mineralocorticoid and
glucocorticoid deficiency, resulting in
hyponatremia and
hyperkalemia, and signs of
cortisol deficiency. The etiology may be immune-mediated destruction of the adrenal cortex,
drug-induced adrenocortical
necrosis (
mitotane),
enzyme inhibition (
trilostane), or infiltrative processes such as neoplastic or
fungal disease. Much less commonly, dogs have signs of
cortisol deficiency, but no
electrolyte changes. This is referred to as atypical HOAC. The veterinarian needs to have a clinical suspicion for HOAC to make a diagnosis in a timely manner. Treatment of dogs with an acute presentation prioritizes correcting the
hypovolemia,
hyperkalemia,
acidosis, and
hypoglycemia.
Fluid therapy addresses most of these issues, but other directed
therapies may be required in the most severe cases. For chronic management, all patients with
Addison's disease will require replacement of
glucocorticoids (usually
prednisone), and most patients require replacement of
mineralocorticoids with either
desoxycorticosterone pivalate or
fludrocortisone. Atypical Addisonians do not require
mineralocorticoid supplementation, but
electrolytes should be monitored in case the need arises in the future. The prognosis for dogs treated for HOAC promptly and appropriately is excellent; most patients die from other diseases. However, if the diagnosis is missed, patients may die as a consequence of HOAC. Thus, knowledge of the hallmarks of
Addison's disease is imperative.