Chances are you either own a senior horse dealing with a condition known commonly as equine Cushing’s disease, or know someone who does. More accurately called pituitary pars intermedia dysfunction (PPID), this disease affects many horses around the world. Here we’ll talk with Steve Grubbs, DVM, PhD, DACVIM, the equine technical manager for Boehringer Ingelheim Vetmedica, Inc., to get the latest facts about PPID.
H&R: What exactly is PPID, and why the name change from equine Cushing’s disease?
Dr. Grubbs: There’s Cushing’s disease in humans, in dogs, and in horses, and though there are some similarities among those, there are many key differences. When you look at the condition anatomically, it’s more precise and descriptive to call it pituitary pars intermedia dysfunction in horses since it’s the pars intermedia portion of the pituitary gland where something has gone wrong, hence the term “dysfunction.” The name equine Cushing’s disease is still commonly used, however, and may be used interchangeably.
In the veterinary community decades ago, we used to think this was a rare condition found only in older horses. Much new information has come out within the last decade, though, and we realize we’re seeing horses with PPID much more frequently. The condition has been around forever; we’re just recognizing it better now. There’s been significant advancement in understanding it over the past five or six years, but there’s still a lot we need to learn. We’ve gained a lot of knowledge about what’s going on with PPID horses, but don’t yet know all the answers.
As certain horses age, they experience a decrease in dopamine production. In a normal horse, dopamine inhibits the pars intermedia of the pituitary gland that controls the release of many of the horse’s hormones. However, in horses with decreased dopamine, the pars intermedia of the pituitary gland is not inhibited, or kept quiet, enough. When the pituitary gland becomes too active with the decrease in dopamine, certain hormone production isn’t kept in check, and we begin to see the clinical signs associated with PPID.
H&R: Are some horses or breeds at greater risk for PPID?
Dr. Grubbs: Horse owners should know that this condition isn’t exclusive to older horses. The more we look for PPID, the more we find it. Yes, it’s more prevalent in geriatric horses, but has been identified in horses as young as 5 years of age. One thing is for sure, though: as a horse ages, his risk factor for PPID increases.
Studies underway will seek to determine if some breeds of horses are more prone to PPID. We’ve tested more than 4,000 horses with at least one clinical sign associated with PPID, plus identified more than 66 breeds and crosses that were PPID-positive. We saw the condition most often in Quarter Horses, but of course, the Quarter Horse dramatically outnumbers other breeds in the U.S., so that doesn’t necessarily mean they’re more prone to it. We’ve seen PPID in everything from ponies (which have a higher incidence) to draft horses (a lower incidence) to everything in between, including Arabians, Morgans, Thoroughbreds, and warmbloods.
H&R: What should a horse owner look for as signs of PPID?
Dr. Grubbs: It’s important to stay tuned in to your horse’s overall health, as clinical signs of PPID at first may be quite subtle. Your veterinarian may see your horse only once or twice a year, but you should have daily knowledge of your horse’s routines, attitude, and appearance. If and when your veterinarian diagnoses PPID, those subtleties are extremely important for you to mention.
In the veterinary field, the clinical signs of PPID have been divided into early and advanced, but those don’t always correlate to age. Early clinical signs can be found in a 12-year-old horse or a 22-year-old horse.
One of the most commonly associated and highly recognizable signs of advanced PPID is an extremely long haircoat all over the body. This coat, which never sheds out or is very slow to shed, is known as hypertrichosis. In the early stage, though, this may appear as longer hair on just portions of the body, such as the neck and legs. It can appear as later-than-normal shedding in the early stages, too. If your horse ever seems to be shedding later than the already-slick horses around him, it may be worth having him checked for PPID.
Another early sign is decreased athletic performance, and though that can be attributed to many other conditions, a PPID horse may exhibit lethargy in connection with the lack of performance. Loss of muscle mass and tone, especially across the horse’s topline, is another early clue. Muscle atrophy increases in the more advanced stages of PPID. Since the horse’s immune system is compromised, a PPID horse is less able to fight off infections, so even small sores may not heal as well.
The most concerning clinical sign, whether in the early or advanced stage, is laminitis, which has the potential to create the most detrimental issues for PPID horses. Laminitis typically appears very gradually in these horses and often goes unnoticed for a period of time, until the horse is extremely sore. Sometimes owners don’t even notice it until it gets to the point that the horse is showing obvious signs of pain. Again, staying vigilant to your horse’s routines and attitude is critical, as this enables you to supply the bigger picture to your vet, in turn allowing him or her to piece all the signs together.
H&R: Can a horse be tested for PPID? If so, what is the procedure for that?
Dr. Grubbs: Testing for PPID has progressed to a simple blood test. If you think you see any of the early or late clinical signs of PPID, have your veterinarian examine your horse and, if needed, pull blood for testing. Pulling blood for resting ACTH (adrenocorticotropic hormone) levels can be conducted any time of day and all year long. Thus if your horse shows any of the early or advanced signs, it’s easy to test for PPID.
An older method, the dexamethasone suppression test, checks for the level of a hormone called cortisol in the blood. Requiring two blood draws on two consecutive days and less accurate during autumn, it’s less convenient than the newer test for resting ACTH levels, but is still used.
H&R: What kind of lifestyle management changes can help a PPID horse?
Dr. Grubbs: Following the diagnosis of PPID in your horse, I’d recommend discussing medical therapy with your veterinarian. Beyond that, treating the whole horse is the best approach. That begins with a thorough veterinary exam and includes conscientious dental care, parasite control, proper nutrition, and tending to basic comforts.
Aging horses, more likely to develop PPID, also need to have their teeth floated consistently. Some PPID horses tend to carry too much weight, but often, older PPID horses tend to run too lean. Untended teeth can complicate keeping weight on these horses, so establish a dental routine with your veterinarian.
PPID horses also tend to harbor more internal parasites than healthy horses. Have your veterinarian run a fecal count to determine type and quantities of parasites, then administer suitable dewormers on a schedule.
Proper nutrition depends greatly on the individual horse’s needs, and varies from one geographic region to another. Learn the body-condition scale, with 1 representing the thinnest and 9 representing the most obese, so that you can communicate accurately with your veterinarian while establishing the horse’s diet. (Note: Find the standard Henneke body-condition score system at bit.ly/bodyconditionscore.)
Monitoring insulin levels is an important part of the horse’s metabolic profile, because increased insulin puts a horse at greater risk for laminitis. Insulin levels can be checked during the same blood draw that checks for resting ACTH levels to determine if the horse has PPID. In our study of more than 4,000 horses, 47 percent of the PPID-positive horses had increased insulin that needed to be managed to help decrease the risk of laminitis.
Some PPID horses with heavy coats will need to be kept body clipped, which helps them regulate their body temperature better. Tend to the comfort of these special horses to make the most of their lives and performance abilities, which can be maintained for many years with careful decisions about their care.
H&R: What does the future look like for managing PPID?
Dr. Grubbs: There’s a huge amount of interest in the PPID horse at this time, and rightfully so. A tremendous amount of new information about the recognition, diagnosis, and management of PPID in horses has come to light in the last few years. We’re now recognizing PPID in younger age groups of horses because we’re aware of the early signs and have newer diagnostic capabilities available. The biggest challenge at this point is to get all this newer information into the hands of horse owners and veterinarians who manage these horses on a daily basis. Horse owners see their horses on a daily basis and can report any changes that might be PPID-related to their veterinarian. I think we all just want to ensure that the most accurate, up-to-date information about PPID gets to horse owners and veterinarians in a timely manner, so we can all work together to manage the PPID horse in the best possible way. It absolutely requires a team approach.