My Senior Horse Podcast: PPID Part 1

In Episode 6 of the My Senior Horse podcast, we start a three-part series on Cushing’s disease, which is now more properly known as pituitary pars intermedia dysfunction (PPID).

In the next three episodes of the podcast, we will cover various aspects of PPID with Hal Schott, DVM, PhD, DACVIM. He is a professor of Large Animal Clinical Sciences at the Michigan State University College of Veterinary Medicine.

What is PPID?

Schott starts the podcast by explaining why equine Cushing’s disease was renamed PPID.

Cushing’s disease in humans was named after Dr. Harvey Cushing, a human physician. That disease was due to a benign tumor in the pituitary that produces additional hormones. One of those hormones (known as ACTH) stimulates the adrenal gland to make more cortisol. A very similar disease is found in dogs.

So, when a similar problem with increased cortisol was found in horses, it was also named for Dr. Cushing.

However, research and time have shown that the diseases in humans and dogs is not as similar as that in horses as was first thought.

For one thing, in horses, the tumor is found on the pituitary pars intermedia rather than the anterior lobe of the pituitary (as it is in humans and dogs).

Schott said there also are similarities between equine PPID and Parkinson’s disease in humans. He said like with Parkinson’s disease, PPID in horses has a dopamine association. Also like with Parkinson’s disease, the issue can be occurring without any obvious clinical signs for a time before the person knows something is wrong.

“In other words, probably many 15-year-old horses out there have enlargement of their pars intermedia,” said Schott.

Studies have shown that about 20% of horses over the age of 20 will start to have clinical signs of this diease. That goes up to about 30% of horses over 30 years of age.

What Are the Clinical Signs?

Schott explained the common and not-so-common things that horses undergo with this disease in the podcast. These include:

Long haircoat that doesn’t shed;
Drinking and urinating more than normal;
Immune system issues (a lower ability to fight off infection);
Laminitis;
Skin issues;
Loss of muscle mass.

He further discussed issues that occur when PPID happens in conjunction with insulin dysregulation. That can contribute to higher probability of laminitis.

What Equids Get PPID?

When asked what equids get this disease, Schott replied: “All of the above.” That means horses, ponies, donkeys, and mules can get PPID.

However, he said ponies are “overrepresented” when it comes to percentage of the population with PPID. But he explained that ponies generally live longer than horses. Since PPID is associated with advanced age, that seems logical.

Schott is collaborating with Dr. Molly McCue at the University of Minnesota College of Veterinary Medicine to look at the DNA of affected horses. They hope to find genetic predictors of PPID.

Then maybe in 10 years, you could do a DNA test to see if the horse has the risk factors for PPID.

Treatments

PPID cannot be cured. However, there are many management strategies that can be used to reduce the problems associated with PPID. Those will be covered in-depth in the next episode of My Senior Horse podcast.

A medication on the market that works very well against PPID in equids is pergolide mesylate that is marketed as Prascend. This is an FDA-approved product. While Schott said it “partly reverses” the disease, it is not a cure. A PPID horse will be on this treatment for life. “Right now, it is the treatment of choice for PPID,” he said.

Do You Suspect PPID?

If you have concerns that your aging horse is showing one or more of the clinical signs of PPID, then talk to your veterinarian.

Schott recommends that you keep notes on each horse you own or manage, and when it is time for the veterinarian to give annual vaccinations, talk about things that concern you. Is your horse drinking or urinating more than normal? Does your horse have places on his neck or legs that don’t shed as quickly as they used to? Does your horse have unexplained slight lamenesses?

Schott said one of the other hormones that is elevated with PPID is beta endorphin, which is an opioid. “It’s the endorphin we think of with a runner’s high,” he explained. “We think sometimes horses with PPID can tolerate more pain because of these hormones that are elevated in their blood.”

Testing for PPID isn’t difficult; it’s a simple blood test. If that is inconclusive in the face of some clinical signs, your veterinarian might use a TRH stimulation test to check the ACTH.

However, if a horse is 17 or 18 years old it doesn’t mean it should be routinely tested or screened for PPID if you don’t see any clinical signs, said Schott.