Cushing's Syndrome

Cushing's disease. I first encountered this disease when doing my riding stable PCEMS. It presents slightly differently in horses than other species due to the way the pituitary tumour acts. 

Cushing's disease is an excess of glucocorticoids e.g. cortisol in the blood circulation. A number of different pathological happenings result in the presentation of this disease. The most common one, and the most important one in horses is caused by a pituitary adenoma secreting ACTH/adenohypophysis hyperplasia.

Clinical signs include:

Normal Glucocorticoid Functions

• Excessive drinking and urination with an increase appetite.
• Trunk obesity with atrophy of skeletal muscle.
• Alopecia, epidermal atrophy and osteopenia.
• Secondary diabetes mellitus. 
• Immunosuppression- increased susceptibility to other diseases.

Horses show different clinical signs because the tumour can be expansile and compress adjacent structures e.g. the hypothalamus and CNS. 

This impairs the hypothalamic areas ability to regulate cyclic hair growth, appetite and body temperature. This leads to the following clinical signs:

• Hirsutism- excessive hair growth.
• Excessive sweat gland secretion (hyperhydrosis).
• Intermittent fever.