Feline Hyperadrenocorticism Study Guide

Overview and Clinical Importance

Hyperadrenocorticism (HAC), also known as Cushing's syndrome or hypercortisolism, is a rare but clinically significant endocrinopathy in cats caused by chronic excessive cortisol production. Unlike dogs where HAC is relatively common, feline HAC accounts for fewer than 200 cases reported in veterinary literature, making it an uncommonly tested but high-yield topic on the NAVLE.

The clinical importance of recognizing feline HAC lies in its unique presentation compared to canine HAC, the strong association with concurrent diabetes mellitus (80-90% of cases), and the distinctive clinical sign of extreme skin fragility that occurs in approximately one-third of affected cats. Failure to recognize this condition often leads to poor diabetic regulation and progressive deterioration.

Etiology and Pathophysiology

Normal HPA Axis Function

The hypothalamic-pituitary-adrenal (HPA) axis regulates cortisol production through a cascade of hormonal signals. The hypothalamus releases corticotropin-releasing hormone (CRH), which stimulates the anterior pituitary to secrete adrenocorticotropic hormone (ACTH). ACTH then acts on the zona fasciculata of the adrenal cortex to produce cortisol. Elevated cortisol levels normally suppress CRH and ACTH through negative feedback.