Horse Health Article - PPID or Equine Cushings’ Syndrome

Image © Paula da Silva/arnd.nl

Most horse owners have heard of Equine Cushings’ Syndrome, with the same image coming to mind - the hairy, overweight old pony. But did you know that this disease can affect many senior horses and ponies, and that being hairy is just one of many symptoms?

So what is Equine Cushings’ Syndrome, or PPID?

PPID is an acronym for Pituitary Pars Intermedia Dysfunction, which describes the area of the pituitary gland in horses that becomes abnormal in horses with this condition. The condition was historically called Equine Cushings’ Syndrome due to the increased levels of cortisol found in these horses, as occurs with Cushings’ disease in humans. However, these conditions are not the same, and we now understand that ACTH (produced by the pituitary gland) is the main driver of a lot of symptoms that horses with PPID suffer.

What causes PPID?

PPID is caused by degeneration of the dopaminergic neurons in the older horse’s hypothalamus (similar to human Parkinson’s disease). The dopamine produced by these neurons normally interacts with the pituitary gland, controlling its production of ACTH (and other hormones).

In horses with PPID, the low dopamine means that the pituitary gland has uncontrolled (and therefore increased) ACTH production.

Image: Kirkwood, Hughes et al. https://doi.org/10.3390/vetsci9100556

What are the clinical signs of PPID?

Unlike the “old hairy pony” stereotype, there are many symptoms of PPID, some of which may go easily unnoticed! PPID affects 1 in 5 horses (and ponies) over the age of 15, with common signs of PPID including:

• Abnormal sweating (hyperhidrosis)

• Delayed shedding/retained hair coat

• Epaxial muscle wastage (loss of topline and neck musculature)

• Recurrent infections (e.g. slow-healing wounds, periodontal disease, high faecal egg count results)

• Lethargy/depression

• Pendulous abdomen

• Frequent laminitis (may be subclinical e.g. horse not showing outward signs of laminitis)

• Degenerative suspensory ligament desmitis

• Excessive urination

How do we diagnose PPID?

PPID is diagnosed by a blood test measuring ACTH levels. This test can be done at any time of year, however it is best performed after the Summer Solstice and before the Autumn Equinox - as this is the time of year that ACTH levels are highest in both normal horses and horses with PPID, therefore provides the best time to guarantee a true positive result.

What is the treatment for PPID?

PPID is treated with a medication called Pergolide mesylate, which increases dopamine levels. The increase of dopamine levels “calms down” the production of ACTH by the pituitary gland, therefore resulting in improvement of symptoms of PPID.

Because the degeneration of the hypothalamic neurons in horses with PPID is an ongoing process (e.g. degenerative with age), it is important that we retest horses on medication for PPID to ensure that the dosage that they are on is “keeping up” with the degeneration, as sometimes dosages may need to be increased over time.

Horses should receive 3-monthly blood tests after starting their medication, until their ACTH is within normal limits, at which point their blood tests can be extended out to every 6 months.

If you think your horse could have PPID, or your horse is currently undergoing treatment and is due for a blood test, please contact us to make an appointment!