[Canine hypoadrenocorticism - an update on pathogenesis, diagnosis and treatment]

Canine hypoadrenocorticism (HoAC) results from a loss of functional adrenal cortex, the most common etiology of which is an immune-mediated destruction leading to an inadequate production of glucocorticoids and mineralocorticoids. The term "atypical" HoAC is used for a subgroup of dogs with either an isolated glucocorticoid deficiency or a combined glucocorticoid and mineralocorticoid deficiency but normal electrolytes. Dogs with HoAC can present with a large variety of clinical signs, ranging from shaking, weakness, and mild gastrointestinal signs to seizures, hypovolemic shock, and collapse. Routine clinicopathologic and diagnostic imaging findings are usually nonspecific and frequently mimic those of other common diseases. However, the absence of a stress leukogram, eosinophilia, hyponatremia, hyperkalemia, and azotemia and small adrenal glands on abdominal ultrasound are characteristic findings in dogs with HoAC. The ACTH stimulation test is currently the gold standard method for diagnosing HoAC. Other endocrine laboratory diagnostics, including the quantification of endogenous ACTH, basal and ACTH-stimulated aldosterone levels, cortisol:ACTH ratio, and aldosterone:renin ratio, may further aid in differentiating between primary, secondary, and "atypical" HoAC. Aggressive intravenous fluid therapy is the cornerstone of treatment in paients with an acute Addisonian crisis because it restores normovolemia and normal blood electrolytes. Maintenance therapy consists of glucocorticoid (e.g., prednisolone) and mineralocorticoid (e.g., des- oxycortone pivalate) supplementation and aims for stable electrolyte concentrations and a clinically well dog. The optimal dose of desoxy- cortone pivalate for a specific dog is determined based on blood so- dium and potassium concentrations by using a standardized protocol. Regular reevaluation of blood electrolytes is required for early identifi- cation of a mineralocorticoid deficiency in dogs with "atypical" HoAC. The long-term prognosis for dogs with HoAC is excellent provided that patients receive adequate treatment and there is good owner com- pliance.