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  • Coastal Equine

A Cushing's Tutorial

Reprinted from by Karen Sweaney

So what exactly is Cushing's Disease? Until a few weeks ago, I only knew that it was a disease that mostly affects older horses with symptoms that include long shaggy coats, pot bellies, and problems with hooves. Sort of like this guy.

Very simply - or not, Cushing's Disease, also called Pituitary Pars Intermedia Dysfunction (PPID), is a disfunction of the pituitary gland. Over time, the pituitary gland becomes over-enlarged and produces too many hormones. Not good. Ask any woman approaching 50 (cough, cough) what it feels like to have your hormones go out of whack.

In particular, horses with PPID produce too much of the hormone called the adrenocorticotropic hormone (ACTH). High levels of ACTH cause an over-production of cortisol. And since hormones have effects on many different organ systems, increased cortisol creates a variety of symptoms like:

  • ​Hypertrichosis (long, curly hair )

  • Delayed haircoat shedding

  • Change in body conformation (muscle wasting and rounded abdomen or “potbelly”)

  • Decreased athletic performance

  • Change in attitude/lethargy

  • Fat deposits, especially along the crest of the neck and over the tail head

  • Laminitis

  • Increased drinking and urination

  • Recurrent infections

  • Abnormal sweating

  • Absent reproductive cycle/infertility

  • Neurologic deficit/blindness

So who gets Cushing's Disease? According to the AAEP, "the average age of horses diagnosed with PPID is 20 years, with over 85 percent of the horses being greater than 15 years of age. Although most common in aged horses, PPID has been diagnosed in horses as young as seven years of age."

I think you can see where all of this is heading. Speedy will be 15 in April. Speedy has never before had an abscess, yet in the past few weeks he's had not one, but two. My vet decided we needed to check for Cushing's Disease.

There are several ways to test for Cushing's: 1) the dexamethasone suppression test and 2) the measurement of resting plasma ACTH concentration. However, one thing to note is that the time of year the tests are done can affect the results. In the fall, horses naturally increase the production of a variety of hormones as the body prepares for winter. Fortunately for Speedy, January is a great time to check ACTH concentrations.​

A normal ACTH concentration is somewhere between 10 and 50. Speedy's ACTH level came back at 56, just outside of the normal range. Some horses can have numbers above 1,000. A lot of things can affect that score - time of day, when the horse last ate, and so on. Even though Speedy's ACTH level was very close to normal, Dr. Tolley felt that it would be prudent to put him on medication. Here's where most owners cringe and ask, "What's that going to cost?" I almost find it funny that Speedy needs a daily medication as I had just this month decided to take my boys off ALL supplements. Joke's on me I guess. The only FDA approved medication for Cushing's Disease is pergolide, brand name Prascend.

I bought Speedy's first box of 160 tablets from a friend who no longer needed it. When that box runs out, I'll need to reorder from somewhere like Allivet as Prascend is available by prescription only. Its per day cost is right around $1.75. Prascend is actually cheaper than the Platinum Performance was, so I can't complain too much.

There is a glitch of course. Pergolide is on US Equestrian's prohibited substance list. Don't even get me started on how incredibly stupid my vet found that rule. One of the worst things you can do for a Cushing's horse is to stop and restart pergolide every other week during show season. There is good news though. As of December 1, 2018, US Equestrian will now allow pergolide if the horse has been granted a Therapeutic Use Exemption (TUE). An explanation of the rule change can be read [on the website]. I've already applied for a TUE, and my vet has submitted all necessary paperwork. When I phoned US Equestrian, the woman I spoke to had no idea how long it takes to be granted a TUE. She said that a panel must review my request. Way to go, US Equestrian. No timeline or answers make me feel great. So that's it. Speedy now has Cushing's Disease which means daily medication, annual bloodwork, and of course getting that pesky TUE. Dr. Tolley wasn't too concerned and neither am I. There's just no cure for getting old.

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