What is Cushing's Syndrome?

Photographs of "Manny" are shown by kind permission of Mr and Mrs J Mason.

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What is Cushing's Syndrome?

Equine Cushing's syndrome is defined as the horse's body producing too much cortisol (hypercorticism).

Symptoms may include a thick, matted, often curly coat, drinking more than usual (polydipsia), urinating more than usual (polyuria), hyperhydrosis (excessive sweating), muscle wasting, a pot-bellied yet 'ribby' appearance, periods of laminitis, chronic mild infections (for example 'boils' on the gums at the front of the mouth), greater susceptibility to disease, and general lethargy and lack of energy.

There are currently different theories as to why horses suffer with Cushing's syndrome. The symptoms are generally thought to arise from pituitary hyperplasia (the cells of the pituitary gland may show abnormal characteristics and be increased in number) or abnormal functioning of peripheral tissues (one theory is based upon increased fat cell production of cortisol). However, adrenal hyperplasia has been observed without pituitary hyperplasia, and links have been made between a condition called Metabolic Syndrome X and Cushing's in which insulin resistance is a key factor.

Treatment tends to concentrate on amelioration of these symptoms. Some available drugs are pergolide (Permax®, Celance®), cyproheptadine (Periactin®), trilostane (Modrenal®) and Agnus castus (Vitex, chaste berry). However, in the first few years, it is often possible to control the symptoms by careful management and feeding.

In recent years, Cushing's syndrome has been divided into categories by some researchers. This has led to terms such as 'pituitary-dependent' Cushing's and 'peripheral' Cushing's being used to describe animals with specific 'profiles'. Both terms still describe an animal with abnormally high levels of cortisol, but the body systems linked to the condition are different. In the former, loss or inactivity of dopaminergic neurons is thought to lead the pituitary hyperplasia mentioned above - this results in the adrenal glands producing more cortisol than normal. In the latter, dysregulation of the enzymes 11beta-HSD1 and 11beta-HSD2 is implicated in increased blood or cellular levels of cortisol, compared to normal.

PED's research centres on there being an identifiable cause behind the problems observed in the endocrine or other body systems. Often, a good quality of life for a Cushingoid horse is described as only being possible for a short, finite period, or something not possible, with euthanasia the kindest option. However, there are many horses which PED believes may be able to have their lives back to almost what they were many years before the onset of obvious Cushingoid symptoms.