Cushings Disease is something that we have a lot of experience with. In fact we have so much experience in identifying, treating and managing Cushings horses we have spent the last few months participating in a clinical study with one of our veterinarians and the manufacturer of the drug Prascend. Many people get confused when they hear the name Prascend, however the actual drug in Prascend is pergolide mesylate, which has been the drug of choice for treating Cushings in horses for many years.
Since we test, treat and live with so many horses with Cushings (more appropriately known as PPID now) we spend a lot of time discussing this with our vets and our clients. I decided it was time to write a series of blog posts that contained the answers to the questions we get asked over and over. Keep in mind in these posts that I will be attempting to explain things in layman's terms, thus I am grossly oversimplifying many of these explanations to allow for ease in understanding of the big picture. In today's post, Part I, am going to attempt to explain what this disease is.
Cushings is one of the most common metabolic disorders, or disorder of the endocrine system, in horses. Cushings disease is now officially called PPID (Pituitary Pars Intermedia Dysfunction) in horses, although most people generally still refer to it as Cushings. In horses Cushings is now referred to as PPID since it was discovered that the mechanism of the disease is different of that in people in dogs.
PPID causes the pituitary gland to overproduce hormones. The pituitary gland, which is sometimes referred to as the master gland, is located at the base of the brain and is made up of three lobes in a horse: pars distalis, pars intermedia, and pars tuberalis. PPID specifically affects the pars intermedia lobe of the pituitary gland, hence the name Pituitary Pars Intermedia Dysfunction.
Under normal circumstances the pars intermedia acts to regulate and suppress the secretion of certain hormones. One of the hormones that is kept regulated via a suppression mechanism is ACTH. PPID is initiated when hypothalamic dopamine producing neurons fail. When this failure occurs the suppression mechanism of the pars intermedia fails.
The failure of the suppression mechanism leads to an increased hormone production in the pars intermedia. The result of this increased hormone production means the hormone levels within the pars intermedia, including ACTH, can be up to 100 times higher than that in a horse that does not have PPID. The cells in the pars intermedia divide and enlarge without regulation, causing the pars intermedia to increase greatly in size. At the same time that the pars intermedia lobe of the pituitary gland is expanding, it forces the other two lobes of the gland to become compressed.
Thus a PPID horse has a greatly enlarged pars intermedia lobe that is busy over producing hormones. This overproduction leads to a variety of symptoms in horses, and rarely do two PPID horses present with exactly the same symptoms. The most common initial symptom we see are issues with the haircoat. The hair is overly long and/or very dry, or the hair doesn't shed properly or shedding is delayed, or some combination of these. The second most common symptom we see is an over-consumption of water. The third most common symptom we see are a poorly functioning immune symptom, or better put as an increased susceptibility to infection. The horses might be prone to skin infections, have chronically puffy and/or runny eyes, and other such symptoms that are easy to write off and attribute to weather and other factors. There are a lot of other symptoms we've seen as well including irregular fat deposits, a lethargic attitude, muscle wasting, etc.
We've seen these symptoms presented very subtly and sometimes in very obvious ways. Sometimes the horse might have only one subtle symptom, other horses start presenting more than one symptom, and some pretty much scream at you "I have PPID, begin treatment now." We've had horses in their early teens test positive as well as older horses. One extremely common misconception is that PPID/Cushings is an "old horse" disease. This has been soundly disproven clinically. As a horse ages the odds of having PPID continue to increase, but PPID has now been clinically verified in many horses as young as five.
In my next post on the topic I'll discuss testing and treatment. I want to state again that in an effort to make my explanations easy to understand I am grossly oversimplifying many things. My point isn't to turn all of us into clinical experts on all aspects of PPID, but simply to help us all understand what it is, how to test for it, treat it and manage horses with it. I hope the information will be helpful to at least a few people!
Lofty and Faune having a particularly relaxing day with George, Gibson and Flyer
a closer look at Lofty and Faune (and George)
Dutch, Blu and Murphy . . .
. . . didn't bother to lift their heads as the turkeys strolled past them
Kennedy and Oskar
Duesy and Remmy (Bruno in the background)
Walden, Hesse and O'Reilly
pony power; Norman, Traveller and Cuff Links
Donovan, Oskar and Johnny
Rocky, Largo and Clayton