Cushing's disease

Author: Lucy Carmichael BVSc MRCVS

What is Cushing’s disease?

Equine Cushing’s is an important progressive hormonal disease which primarily affects horses over the age of 10, reportedly affecting 1 in 5 horses over the age of 15. Its correct veterinary term is Pituitary Pars Intermedia Dysfunction or PPID. This name is associated with the cause of Equine Cushing’s disease, where the pars intermedia of the pituitary gland in the brain receives a lack of inhibition and becomes enlarged. This in turn leads to a marked increase in several hormones, causing numerous different effects around the body.

Symptoms

Symptoms can be varied and may be subtle in some cases. Generally, the classic clinical signs of Cushing’s disease are:

• Laminitis

• Increased coat length/curly coats

• Abnormal shedding of coats

• Weight loss / muscle loss

• Increased drinking and urination

• Lethargy

• Increased sweating

• Increased susceptibility to infections

Testing

Diagnosis of the disease is based upon the clinical examination by your veterinarian, if appropriate, it is likely that a blood sample will be taken. The simplest blood test measures your horse’s baseline ACTH level. ACTH is a hormone which is naturally produced but is present at increased levels in horses with Cushing’s disease. Sometimes, a more specific test may be deemed necessary. This is called a TRH stimulation test; in which a baseline blood sample is taken, TRH is then administered and shortly afterwards another blood sample is taken to assess the horses response.

A blood sample is taken from the jugular vein

Treatment options

Careful management of horses and ponies with Cushing’s disease is essential. Cushing’s often walks hand in hand with laminitis, and therefore dietary restriction of glucose by feeding low glucose feeds, soaking hay for at least 8 hours to reduce the sugar content and using a muzzle if appropriate would be sensible actions. Further to this, monitoring comfort when walked out, checking your horse’s hooves for warmth and checking if their digital pulses (felt over the fetlock joint) are increased can be useful to add to your daily checks.

There is a medication available for the treatment of Cushing’s disease, and your veterinarian will advise if this is appropriate for your horse. Repeated blood samples, usually annually, are recommended to ensure that your horse’s Cushing’s is controlled, and that their medication dose is appropriate.