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Cushings

Cushings disease is also known as pituitary pars intermedia dysfunction (PPID). It is a condition affecting part of the brain called the pituitary gland. This part of the brain makes hormones including one called ACTH and this disease causes excessive amounts of this hormone to be in the blood. It is a condition mostly associated with ageing horses with the average age of diagnosis being 19 years, although it can be diagnosed in horses 7-10 years of age plus.

Symptoms

There is a wide range of symptoms relating to excessive ACTH levels which may include one or a few of the following, or in some cases there are no obvious outward symptoms, and it is found on screening blood tests:

Lethargy

Not quite themselves.

Drinking and urinating more

Infections

Which either don’t resolve as we expect or are recurrent – this is due to a suppression of immunity.

Increase in faecal worm egg count

Again due to immune suppression.

Long haircoat which may be curly and delayed shedding of winter fur

Sometimes the coat just loses quality and becomes stary and they may be more prone to catching lice.

Increased sweating

Laminitis

Cushings can cause laminitis.

Loss of topline

Due to muscle mass breaking down.

Pot belly

Due to the loss of muscle strength and topline cushingoid horses can appear potbellied. This is typically associated with old age but is most likely due to cushings.

Diagnosis

A blood test can be taken to measure the ACTH hormone levels. A horse’s ACTH levels naturally fluctuate throughout the year with a natural elevation in the autumn and the laboratory now have accurate adjusted reference ranges to be able to interpret these levels accurately.

In some cases, a resting ACTH blood test is not accurate and may produce a false negative result. If there is a high clinical suspicion of cushings but a negative resting ACTH result, we may perform a TRH stimulation test. This is a dynamic test where the ACTH level is measured before and again 10 minutes after an injection of a hormone called TRH which stimulates the ACTH pathway. This is the most accurate cushings test.

Treatment

Treatment is with a medication which will be required for the rest of the horse’s life. There are a few available treatments with the most common being daily pergolide tablets (Prascend) or weekly cabergoline injections.

The pergolide tablets are given once or twice daily depending on the individual response. These are mostly well tolerated but some horses go off their food. If this happens a dose adjustment may be indicated or if this does not work either, then alternative treatment should be considered.

The cabergoline injections are once weekly under the skin injections which can be given by the owner. These are particularly useful in horses who do not tolerate pergolide, require high doses of pergolide to maintain control of the cushings or when owners prefer the convenience.

Management

Managing the consequences of cushings can help to keep the risk of complications to a minimum and keep the horse more comfortable. This can include clipping of the hair coat to prevent overheating, keeping up with regular worm control and maintaining excellent farriery and dental care. Diet is also important – with the increased risk of laminitis the aim should be to keep sugar and starch levels low but with the loss of topline some nutritional support is helpful for maintaining condition. This is best achieved with protein and fats as opposed to sugar and starch, it is best to seek nutritional advice for feeding cushingoid horses to provide optimal benefits and minimise risks.

Regular blood tests are invaluable in helping to monitor the disease levels and to see if the current treatment dose is correct or whether it needs to be adjusted. Cushings disease may progress despite the treatment and so dose increases are fairly common over time.

Prognosis

Although it is a lifelong condition which cannot be reversed, most horses with cushings can live a normal and long life with medication and management. The key is reducing the side effects of the disease such as infections and laminitis which may have more serious implications.