AKA Equine Pituitary Adenoma

As many owners of horses & ponies will testify the quality of life of our animals is paramount. Thus it is very perplexing as an equine veterinary surgeon in this animal loving country that so many cases of this distressing disease either go unnoticed or more alarmingly untreated when diagnosed.

This very simple blog is just a basic synopsis of what to look out for if you are suspicious that your horse has Cushing’s. Then at the end a short overview of the currently available medical treatments are briefly evaluated based on current veterinary evidence.

What is Cushing’s disease of the horse?

Put very simply Equine Cushing’s disease/syndrome is an excess production of steroid by the adrenal gland of the horse.

Why does it happen?

To explain why it happens one has to understand the normal production of steroid in the body, remember we all need some steroid to live and function properly and our horses are no different.

Cortisol (the steroid produced by the adrenal glands of the horse) is produced when it is told to do so by a hormone called ACTH released from the brain. This production of ACTH is stopped once cortisol is produced, so the cortisol acts as a controlling balance mechanism within the body telling the brain to reduce the production of ACTH.

When this mechanism goes wrong, as in Equine Cushing’s disease/syndrome, that’s when the problems start. In Cushing’s disease/syndrome it is usually a problem in the brain of the horse. A small tumour causes an unregulated production and therefore release of ACTH.

This then tells the adrenal gland to produce cortisol but unlike in the normal horse the newly produced cortisol does not tell the brain to shut down the ACTH production. Therefore ever increasing levels of ACTH allow more and more steroid to be produced and enter the blood leading to the disease of Equine Cushing’s disease/syndrome and all of its distressing clinical signs.

So what are the suspicious signs of Equine Cushing’s Disease/Syndrome and what horses are more likely to be affected?

The following are some of the more commonly seen signs with Equine Cushing’s disease/syndrome but it is by no means an exclusive list, nor will every horse with Cushing’s exhibit all of these signs. Indeed there are other clinical signs not mentioned and it is for these reasons that this blog should in no way replace the clinical judgement of your vet with whom you should liase closely.

Secondly if you are going to successfully get to the bottom of this disease then you, your vet and your farrier (most likely) will have to work very closely to treat and manage this disease.

Some frequently reported signs:

• Not an uncommon disease of horses over 15 yrs (rare in the younger horse)
• Greatest incidence amongst the 20-25 year olds
• Mares seem to more affected (reasons not known)
• Polydipsia (drinking more) & polyuria (peeing more) these often go unnoticed
• Glycosuria (glucose in urine)
• Hirsutism (abnormally dense or hairy coat)
• Hair abnormally long, curly or brittle
• Density of hair can be exceptionally high
• Normal seasonal shedding of hair often does not happen
• Sweating and or weight loss is often common
• Not easy to notice amongst the dense coat
• Infections (respiratory/tendon sheaths/joints/oral ulcers) are not uncommon
• Minor wounds often fail to heal or heal poorly or very slowly
• Dramatic weight loss/muscle weakness/lethargy are commonly noted
• Reproductive cycles in mares are often interrupted or are abnormal length
• Some mares will lactate while not pregnant or nursing foals
• Laminitis (frequently) & colic are often seen in the later stages of this disease
• Bulging fat pads are often seen above the orbits of the eyes
• Some horses may even go blind (albeit this is not common)

So how do I find out if my horse has this disease?

If you are worried about your horse having Cushing’s then you must liase with your vet. He or she will be able to add to the details described above. They may also help rule out other common causes to the signs described above.

Your vet will have a fair clinical suspicion (as will you) that this is a possible cause and thus an accurate diagnosis may be sought. This will involve a blood sample(s).

There are many tests that can be done but from my experience the most accurate blood tests involve testing for these four parameters on an overnight fasted horse:

1. Basal cortisol levels
2. Insulin levels
3. Glucose levels
4. ACTH levels

1. This ACTH sample must be spun/separated and frozen within a half hour of sampling and must be sent frozen to the laboratory. This is the current Laminitis Trust recommended blood test method of diagnosing this form of Equine Cushing’s disease.

What can I do once my horse has been diagnosed with Cushing’s?

There is no surgical cure for Equine Cushing’s disease/syndrome as it is a tumour in a part of the brain that is extremely difficult to get access to. Thus medical and farrier management is the current treatment of choice although herbal treatments such as “Monks Pepper” may also be investigated. Further details of this possible option can be obtained on request, please email us at info@vetmedsplus.co.uk

Like all medical problems it is often better to treat earlier than later. There are a few treatments that are useful but unfortunately all are expensive. Another problem is that there are no currently licensed products for the treatment of this disease in this country. It is my understanding that this may change in future and we will post them if or when they become available.

There are a few human medicines that are not licenced for use in horses although have very good results in helping control Cushing’s Disease. As they are not licenced for use in horses we are unable to list their names in this article.

I hope you have found this useful. If you have any comments please submit them to our blog and we will publish them on the website. If you have any questions please feel free to email us at: info@vetmedsplus.co.uk

Sincerely, The Vetmedsplus Large Animal Vet