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What is cortisol? Why does the
horse have such a thick coat? Why does the horse
drink more? What causes the muscle
wasting? Why are there sometimes fatty deposits in
unusual places (e.g. over the eyes)? Why is
the horse susceptible to
infections? How does cortisol cause
laminitis? |
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.
Photographs of "Manny" are shown by kind permission of Mr and Mrs J Mason.
If you've ever owned a horse experiencing laminitis, especially repeated laminitis, you'll know there tends to be one thought, "This needs to be stopped asap".
The problem is that no-one seems to know the answer.
Researchers at PED believe that laminitis is caused by a body imbalance that can be put right. This concerns the relationship of certain chemicals, called biogenic amines, or neurohormones, and may be caused by an immediate situation (e.g. too much grass) or a progressive, cumulative development over time (e.g. Cushing's disease).
The important thing is to know what imbalance might be present in each individual horse order to select the most effective treatment. We can now do this from a small blood sample, sent to our lab.
As many people know, susceptibility to laminitis tends to increase as a horse becomes older. The same tests may be used to monitor your horse, to have an objective way to look at how his/her management, feeding and other routines are affecting the body internally. Your vet can take the blood sample during a routine visit, e.g. before inoculations are given, to keep costs down. The sample needs to be collected first thing in the morning.
To access this service from PED, contact your vet and ask to schedule a visit for a blood sample to be taken for a PED® BAR™ (biogenic amine ratio) test.
It may take considerable time and TLC to achieve, but it is possible to give many horses diagnosed with Cushing's disease (and associated laminitis) a very good quality of life.
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As many people know, the history of laminitis is as long as the history of the horse.
It is a painful and debilitating condition in which the attachment between the Pedal Bone (or third phalanx, P3) and the internal tissue supporting it inside the hoof is degraded. Due to this lack of support, the whole P3 may sink downwards inside the hoof towards the sole, or, more often, 'rotate' so that the toe of the bone moves backwards and downwards within the hoof capsule towards the sole. There is published work supporting a better prognosis for horses with 'rotation' than with 'sinking', although both may be present to some degree. Any number of hooves may be affected. Quite often it is all four, even if the pain appears to be predominantly in the front hooves.
Unfortunately, there is still no sure way to tell whether a particular horse may survive laminitis with little damage, or be in a position requiring euthanasia within hours. All cases should be treated as an emergency and radiographed (x-rayed) as soon as possible.
There are merits to many of the remedial shoeing techniques available to support the P3 during active laminitis; however, experience also shows that some horses fare best 'barefoot' with no human interference! Each individual animal should be treated as just that: an individual. What works for one, may cause intense pain in another. The ideal situation is the owner, usual vet and usual farrier discussing the best course of action as a team. As long as the animal has the chance of returning to a good quality of life, it is worth trying to save it.
Laminitis is NOT always the owner's fault. It may be triggered by any of the following:
Peripheral Cushing's, Metabolic Syndrome, Syndrome X...these terms all basically describe the same condition. 'Syndrome X' was originally proposed in human medicine, by Gerald Reaven, and consists of the following symptoms:
The following factors worsen the condition:
Many of these symptoms have not been fully examined yet in horses, but it is acknowledged that a state very similar to human Syndrome X may exist.
Additionally, medical articles have been published in which metabolic syndrome is described as a mild case of Cushing's syndrome. Other research proposes a chain of events from insulin resistance and glucose tolerance problems, to metabolic syndrome, to full-blown Cushing's syndrome.
The photograph of Oscar is copyright of mono lifestyle photography and shown by kind permission of Anna Bradley.