The Diagnostic Approach of Hypercortisolism in the Dog

Introduction
Hypercortisolism is a common condition in dogs and can be defined as the physical and biochemical changes that result from prolonged exposure to inappropriately high plasma cortisol concentrations, whatever its cause. this disorder is often called Cush- ing’s syndrome, after Harvey Cushing, the neurosurgeon who first described the human syndrome in 1932.

Cushing’s syndrome is frequently iatrogenic, in most cases due to administration of glucocorticoids for the treatment of a variety of allergic, autoimmune, inflammatory or neoplastic diseases. this abstract will focus on the diagnosis of spontaneous hypercorti- solism. in 80-85% of the spontaneous cases hypercortisolism is adrenocorticotropic hormone (aCtH)-dependent, usually arising from hypersecretion of aCtH by a pituitary corticotroph adenoma. the remaining 15-20% of cases of spontaneous hypercortiso- lism is aCtH-independent and result mainly from autonomous glucocorticoids hyperse- cretion by an adrenocortical tumor.

Diagnosis of hypercortisolism
The endocrine diagnosis of hypercortisolism depends on the demonstration of two principal characteristics: (1) increased production of cortisol, and (2) decreased sensitiv- ity to glucocorticoid feedback. Measurement of a single plasma cortisol concentration has little diagnostic value because the pulsatile secretion of aCtH results in variable plasma cortisol concentrations that may at times be within the reference range. there are two ways to overcome this problem: (1) to test the integrity of the feedback system, and (2) to measure urinary corticoid excretion. [...]