What is PPID?

A few years ago PPID or Equine Cushing’s Disease was considered a rare hormonal disease in horses. Now it is thought to affect over 20% of horses over the age of 15¹ and is a condition recognised almost daily in equine veterinary practice.¹

PPID is a hormonal disease caused by changes in the pituitary gland. The pituitary gland is located at the base of the brain. It is normally regulated by a substance called dopamine and produces a variety of hormones. These hormones are distributed around the horse’s body via the bloodstream and play an important role in maintaining and controlling a variety of bodily functions.

Horses and ponies with PPID don’t produce enough dopamine, and this means that the pituitary gland is unregulated, and produces too many hormones. One of these hormones is called ACTH, but it is likely that there are many others.

The clinical signs of PPID are likely to be associated with these elevated hormone levels, but the exact link between the elevated hormones and the signs of the disease is still unknown.¹

It is important to note that although Cushing’s disease in people and dogs is similar to Equine Cushing’s, they are actually different diseases with different symptoms and treatments.

Signs of PPID

What are the clinical signs of PPID?

Laminitis - Recurrent laminitis
Hypertrichosis (an abnormal hair coat which can range from mild changes in coat shedding or colour during the early stages of disease, through to a curly overgrown coat in the later stages)
Abnormal fat distribution: pot belly, loss of muscle condition and a wasted topline
Fat pads around the eyes (peri-orbital fat)
Excessive/patchy sweating
Increased drinking and urination
Lethargy/poor performance
Recurrent infections eg foot abscesses, sinusitis

Laminitis and PPID

Why does PPID cause laminitis?

PPID is a common cause of laminitis: in one study up to 70% of horses with laminitis were shown to have high levels of the hormone associated with PPID.²

The exact link between PPID and laminitis is not fully understood, and research into this area is ongoing.

One theory is that PPID increases the risk of a horse developing laminitis because most horses with PPID show an exaggerated insulin response (high insulin levels) in response to ingested glucose.¹ The theory supposes that when a horse with PPID eats grass with a high sugar content, they develop high levels of insulin in their blood, and these high insulin levels cause laminitis. Although it is well established that very high levels of insulin (insulin resistance) will cause laminitis³ the picture is complicated by the fact that not all horses with PPID will have insulin resistance, and not all horses with insulin resistance will have PPID.

It is thought that sub-clinical PPID (PPID with no obvious clinical signs) will have been present for several months to years prior to laminitis developing.¹

PPID diagnosis

The simplest and most common test for PPID is the basal or resting ACTH test. To perform this test your vet will take a blood sample from your horse and send it to a laboratory. The results of the test can be compared to reference ranges (which will change with the seasons) to confirm the presence or absence of PPID.

However the basal ACTH test is not perfect and will not always pick up all cases of PPID. If your horse tests negative for PPID but continues to show clinical signs of the disease it may be worth re-testing at a later date.

Sometimes the results of this test are not clear cut. The test results can fall into a ‘grey zone’ between a clearly positive and a clearly negative result. If this happens to your horse your vet may recommend re-testing after 3-6 months, or performing an alternative test called a TRH stimulation test.

The measurement of serum insulin and glucose is often recommended in PPID cases and acts as an indicator of both laminitis risk as well as the likely outlook for the patient.¹

PPID treatment

How is PPID treated?

There is only one veterinary medicine which is licensed for the treatment of clinical signs associated with PPID in horses, and which has therefore demonstrated both benefits of treatment as well as a suitable safety profile. This treatment, available from your veterinary surgeon, helps to normalise hormone secretion from the pituitary gland into the bloodstream.

As this treatment affects hormone production, there is usually a short lag between beginning treatment and seeing your horse return to normal in terms of clinical signs. It usually takes between 4-12 weeks to see a clinical benefit of treatment, although in some unusual cases it can sometimes take several years before a benefit is seen.¹