Cushing's Disease - It's more than just a fuzzy pony!
What is PPID ("Cushing's disease")?
It's a degenerative condition of the part of the brain that controls the body's cortisol production ("PPID" stands for "Pituitary [the part of the brain affected] Pars Intermedia [the part of the pituitary that is not working correctly] Dysfunction".
Think of it as a light switch that is always on and cannot be turned off: the pituitary normally tells the adrenal glands when to make cortisol, but when it becomes dysfunctional there is no signal coming to the adrenals anymore to shut down for a while.
What causes PPID?
There is no known cause per se. Oxidative stress may play a role, as may genetics, but really we have no good answer at this time.
Who gets PPID?
Traditionally we thought of PPID as a disease that exclusively affected older horses and we diagnosed it by looking at the horse's haircoat: if it was long and curly, and poorly shedding at the end of winter, we figured it had PPID. As testing methods have improved, we are finding horses without those tell-tale signs to have the early stages of the disease. Sometimes these horses are quite young, the youngest one we have ever diagnosed was 9 years old. We have seen just about all breeds in our practice affected, from Miniatures to Percherons and everything in between.
What are the symptoms of PPID?
Very early on there may be no obvious symptoms at all. One sign that often makes us suggest testing is a loss of topline - all of a sudden the horse "looks old". Horses with a greasy feel to their skin and slightly dull looking coat may have PPID. I am also very suspicious of PPID in any horse that founders, as I find that common triggers of laminitis (such as too much grass or acute Lyme disease) will more likely send a PPID horse "over the edge" than a non-PPID horse. And of course the shag-carpet appearance is a dead give-away, as nothing else will make a horse hold on to its winter hair all the way through summer, or make a normally non-curly horse have a curly coat.
How do I know if my horse PPID?
The best test available to us is called a "TRH stimulation test" (TRH stim for short). This test involves injecting a substance (protirelin) intravenously, then waiting 9 1/2 minutes before drawing a blood sample. This sample has to get cooled immediately, spun down as soon as possible and frozen before sending it to the lab. Protirelin causes the brain's stored ACTH to be released so that we can measure the total amount of ACTH available at the time of testing, instead of just the amount currently in circulation. This avoids false negative results and is the most reliable test available to us at this time. There are naturally occurring seasonal differences in how much ACTH the brain produces, so in the fall testing is not recommended due to an uncertainty of how to properly interpret the results.
What treatments are available?
The FDA approved treatment for PPID is a medication called pergolide (trade name Prascend https://prascend.com/ ). It will alleviate symptoms of PPID in the vast majority of patients. There have been anecdotal reports of treatment failure, although we have yet to see one. Compounded pergolide is also available, but because the substance is highly susceptible to deterioration from oxygen exposure we do not prescribe oral compounded pergolide, as it is impossible to tell how much active drug is actually still contained in any given dose after a while. There also is a "cousin" to pergolide, cabergoline, which is available as a compounded injectable formulation. We have prescribed this in cases of horses absolutely refusing to take the Prascend pill (you'll find some hacks on how to get 'em down the hatch below). However, as with all compounded preparations, the actualy concentration of the drug on the outset may vary since the compounding pharmacies are not a strictly monitored as an approved FDA production facility.
More information on PPID treatments, including Chasteberry, can be found here: https://www.ecirhorse.org/treatment-ppid.php
Why can't I just clip my horse's coat instead of treating it?
Not treating a PPID horse and just managing the clinical symptoms is an acceptable option in our personal professional opinion so long as laminitis is not part of the clinical presentation! Laminitis (aka "founder") is an excruciatingly painful and debilitating condition, so once a horse founders we feel that it is cruel to not treat the underlying cause. As long as laminitis is not part of the picture an owner may chose to manage and monitor, as long as the following caveats are observed:
What other effects does PPID have on my horse?
PPID causes a chronically elevated cortisol level in the horse. This in turn can lead to
Reduced immune function, making the horse more susceptible to infections
Reduced integrity of connective tissues, making the patient more prone to ligament and tendon breakdown as well as dental disease, because teeth are held in their sockets by periodontal ligaments
Loss of muscle mass, often times substantial, leading to more strain on joints and making arthritis worse
Changed mental state (depression, "grumpy old horse" syndrome)
I have decided to treat my horse but he won't take that darn pill!
Apparently Prascend is not the most tasty treat to horses. Many will take it without a fuss, while others flat-out refuse ANYTHING that could POSSIBLY contain the pill. First try to just place the pill on top of the regular feed. Once it goes down with the first bite the battle is usually won. We also recommend finding out prior to starting treatment which treats your horse really likes. Think outside the box - how about bananas? Peanut butter? It seems that Prascend gets more unpalatable once it's wet, so dry or fatty hiding places may work better than the traditional apple sauce or piece of carrot. If just putting it on top of the regular ration is not working read on for some tricks that have worked for us and some of our patients:
soaked beet pulp (put pill right on top just before feeding) - Aly's favorite
a slice of sandwich bread torn in half and balled up, one ball with and one ball without the pill (thanks, Lynda Lawrence and Romy!)
pieces of banana
and our favorite: the pill fits perfectly into the hole of a life saver (Alice McClure figured that one out, we think it's brilliant!)
What side effects does the treatment have?
Most patients experience no negative side effects when they start the treatment. Our clients will often tell us that the horse is acting 10 years younger, is much brighter, and has more energy (not to mention that it just lost enough fur to stuff a pillow!). But some horses do experience some side effects, which stop right away if the dose is reduced or the medication is discontinued altogether. The most common problems we see are inappetence, diarrhea, and depression. If any of those occur work with your veterinarian to find a solution!
More resources on PPID
