Cushings Disease

The illness 'cushings disease' can occur in various animals (e.g. horses, dogs, people). The form which occurs in horses (and other equines, such as ponies) is called Equine Cushings Disease, which is sometimes abbreviated to ECD.

ECD is caused by the pituitary gland producing too much hormone, resulting in over-stimulation of the adrenal glands, which in turn produce excessive amounts of steroids. Although a certain level of steroids is normal, this excessive amount results in various health issues (see Symptoms and Diagnosis below). The most common cause of the pituitary gland producing excessive hormones is the development of a benign tumor on the gland or abnormal enlargement of the pituitary associated with aging. More recent studies indicate that the disfunction of the pituitary gland can be caused by inadequate production of dopamine due to the dopamine-producing cells in the brain aging and dying. Whatever explanation one follows, ECD is an illnesses which results from excessive hormone production. Alternative names for ECD are:

  • The term HYPERADRENOCORTICISM is sometimes used instead of ECD or cushings disease (HYPER = extreme, ADRENO = related to adrenal glands, CORTIC = refers to outer layer, in this case of the adrenal glands, ISM=process).
  • Other names include Equine Pituitary Gland Hyperplasia (EPGH), as well as Pituitary Pars Intermedia Dysfunction (PPID).

As horses become older (e.g. over 15 years), they become increasingly likely to develop ECD, although the condition has been found in horses as young as seven years. It is also more common in ponies than in horses. Studies have shown that many horses which have the condition have not been diagnosed with it, either because the symptoms have been ignored or because the symptoms have been incorrectly attributed to a different illness. Consequently, the condition is much more common than indicated by diagnosis.

Cushings Disease is named after Harvey Cushing, an American brain surgeon, who first defined the basis of this illness.

Symptoms and Diagnosis

Signs of ECD are as follows; note that most horses with ECD will display only some of these symptoms, especially during the earlier stages:

  • Coat. Coat becoming curly. Failure to shed coat in Spring. Coat becoming longer and thicker than normal. Color changes, in particular coat becoming lighter.
  • Weight and Appetite. Horse loses weight, despite increased appetite and increased food consumption.
  • Sweating. Horse sweats more than normal.
  • Diabetes and Drinking. Horse may become diabetic, which can result in increased water consumption and consequently increased presence of urine in stall.
  • Filling above eyes. Horses normally have depressions above the eyes (particularly visible when the horse chews) but with ECD these depressions tend to fill in.
  • General depression. Horse looks depressed and ill, losing coat shine.
  • Laminitis. Eventually, ECD will cause the horse to have laminitis.
  • Body Shape. Changes in body shape. Loss of muscle on back and neck, while abdomen becomes pendulous.
  • Immune system. General decrease in resistance to infections and parasites (e.g. worms).

A veterinarian experienced in ECD may make a diagnosis based on observation, which can be verified by a blood test. Urine and blood tests can also be used to rule out other possible causes of these symptoms.

Laminitis and ECD

The amount of hormone produced by the pituitary gland is affected by the the amount of daylight. This is because the pituitary gland is influenced by the pineal gland (known as 'the third eye'), which reacts to day length. Consequently, symptoms of ECD, in particular laminitis, are generally more severe in the autumn (as days shorten) and winter. Since the most common cause of laminitis (founder) is carbohydrate-overload, often due to spring grass, its occurrence in winter (unless caused by excessive grain) is a particular indication of cushings disease. 

Treatment

ECD cannot be cured. However, the hormone levels can be regulated through medication, thereby controlling the condition. Some of these drugs can cause or aggravate liver disease, so one should not overdose, and a blood test of liver function prior to starting treatment and periodically thereafter is advisable with liver-affecting medication. 

One also needs to treat the secondary problems (e.g. diabetes, laminitis) which develop as a result of ECD. Also watch closely for infections or illnesses, which are more likely to occur and more difficult to clear, due to a depressed immune system. Likewise, injuries are less likely to heal on their own so need to be kept clean and may need antibiotics.

The horse can also be made more comfortable and its quality of life improved through management of the symptoms. For example, if it does not shed its coat in spring, resulting in the horse having an excessively hot coat during summer, one can clip the coat.