Difficult Cases of Canine Hyperadrenocorticism

Introduction
A hyperfunction of the adrenal cortex, i.e., hyperadrenocorticism, may result in hyper- cortisolism, hyperaldosteronism and/or hyperandrogenism. Spontaneous hypercortiso- lism is a common disorder in dogs and can be defined as the physical and biochemical changes that result from prolonged exposure to inappropriately high plasma cortisol concentrations. in 80-85% of the spontaneous cases hypercortisolism is adrenocortico- tropic hormone (aCtH)-dependent, usually arising from hypersecretion of aCtH by a pituitary corticotroph adenoma and rarely due to ectopic aCtH-secretion. the remain- ing 15-20% of cases of spontaneous hypercortisolism is aCtH-independent and result from autonomous hypersecretion of glucocorticoids by an adrenocortical adenoma or adenocarcinoma. in addition to an adrenocortical tumor, aCtH-independent hypercor- tisolism can be caused by bilateral (macro)nodular adrenocortical hyperplasia as a result of aberrant adrenal expression of either ectopic or overactive eutopic hormone recep- tors.

Hypercortisolism due to ectopic ActH secretion
Ectopic aCtH hypersecretion has been documented in an 8-year-old German shepherd dog. the uCCrs and plasma aCtH concentrations were very high and not suppressible with dexamethasone. these findings were initially interpreted as being consistent with pituitary-dependent hypercortisolism (pDH). However, histological examination of the tissue removed by transsphenoidal hypophysectomy did not confirm the presence of an adenoma. Within two weeks after hypophysectomy the clinical manifestations were exacerbated and both the uCCr and plasma aCtH concentration were further increased. Ct of the abdomen revealed a tumor in the region of the pancreas. Laparot- omy revealed a 5-mm nodule in the pancreas, a 3-cm metastasis in an adjacent lymph node, and metastases in the liver. partial pancreatectomy and excision of the lymph node were performed, and a neuroendocrine tumor with metastasis in the lymph node was diagnosed by histopathology. Based on this report, ectopic aCtH secretion should be considered in cases of severe hypercortisolism in which plasma aCtH concentrations are very high and are not suppressible with high doses of dexamethasone, and in which diagnostic imaging does not reveal a pituitary tumor. in patients with pDH intravenous administration of 1 μg corticotropin-releasing hormone (CrH) per kg body weight results in a significant increase in plasma concentrations of aCtH and cortisol, but in patients with ectopic aCtH secretion CrH does not increase these plasma hormone concentrations. the neuroendocrine tumor causing the ectopic aCtH syndrome may be detected by a whole-body scan, but in human patients with ectopic aCtH syndrome the tumors are frequently small and often not found. [...]