About three decades ago (as I recall), it was noticed that some Peruvian Paso horses were starting to break down, especially in their hind limbs. As the horses got older their fetlocks began to sink into the ground. Ultimately, the horses became unusable, and many had to be euthanized. The condition was given a name – Degenerative Suspensory Ligament Disease (DSLD) – and a new disease was born.
Since that time, much has been learned about this very curious, and very incurable, condition. What was once thought to be a condition limited to the Peruvian Paso breed, has, in fact, been determined to be a debilitating disorder of a number of breeds, including Peruvian Pasos, Peruvian Paso crosses, Arabians, American Saddlebreds, American Quarter Horses, Thoroughbreds, and some European warmbloods. A disease that was thought to affect only the suspensory ligament has, in fact, been found to be a systemic disorder, with identifiable characteristics that can help veterinarians make an accurate diagnosis (more on that in a bit).
DSLD isn’t a problem that’s limited to the suspensory ligament. It’s a disease of the whole horse, a systemic disorder that involves tissues and organs that are made up of a kind of tissue called connective tissue. Connective tissue is tough tissue that connects, supports, binds, or separates other tissues or organs; examples include tendons and ligaments, but also the tough membrane that surrounds muscle cells (and is hard to chew if you find some in your steak). In DSLD, the problem isn’t with the fibers of the ligament itself, rather, it’s an abnormal accumulation of substances called proteoglycans between the fibers of the
affected tissues. Proteoglycans are a sugar-protein complex that is normally found between cells and provides structural support; in DSLD, there’s just too much of an otherwise good thing. In fact, since it’s not just the suspensory ligament that’s the problem – may other tendons and ligaments besides just the suspensory ligament are involved - it’s been proposed that the disease be called equine systemic proteoglycan accumulation (ESPA), as opposed to DSLD.
UNRELATED VERNACULAR ASIDE: You can call it ESPA, but most people in the barn won’t know what you’re talking about, since the new name seems not to have caught on just yet.
Now, back to the disease…
DSLD is thought to run in families. It’s somewhat somewhat similar to some hereditary diseases that affect connective and musculoskeletal tissues in people such as Marfan syndrome (on a completely unrelated note, some people think that Abraham Lincoln may have had Marfan syndrome), or Ehlers-Danlos syndrome. Like these diseases, DSLD ultimately leads to breakdown of connective tissue.
As the supporting connective tissues of the limb break down in affected horses, you might see any number of clinical signs. The fetlocks drop towards the ground, pasterns move towards horizontal, and hocks and stifles straighten out. Sometimes affected horses have a hard time
standing when the opposite leg is held up due to the pain. You can sometimes feel enlargement and/or hardening of any or all of the suspensory ligaments (even though the problem is horse-wide). DSLD frequently leads to persistent, incurable lameness, especially of the hind limbs. The disease is slow, and progressive, and affected horses are often ultimately euthanized due to breakdown of their limbs – a horse that’s walking on the ground with its fetlocks is not pretty to see.
Diagnosis of DSLD is typically based on family or breed history (horses that have DSLD tend to breed more horses with DSLD), clinical examination of the horse with sinking fetlocks, and ultrasonography of the affected ligament(s), which shows mostly that the tissues are breaking down, but for no specific reason. In fact, up until a few years ago, the final diagnosis of DSLD was always pretty much a matter of waiting and seeing what happened to the horse – if they got really bad, and nobody could do anything about it, bingo, the diagnosis was made (albeit a bit late).
In 2006, however, some very clever investigators at the University of Georgia started to unravel the mysteries of the disease. As good scientists like to do, particularly when they’ve found something really revolutionary (but even when they are just trying to get tenure), they’ve published their findings.
CLICK HERE to see the article, “Degenerative suspensory ligament desmitis as a systemic disorder characterized by proteoglycan accumulation,” published from the Department of Large Animal Medicine at the College of Veterinary Medicine at the University of Georgia.
Out of this work came a technique to suggest a diagnosis for DSLD, based on biopsy of the nuchal ligament, a big, tough ligament that connects the poll to the withers, and helps hold the horse’s head an neck in position. Don’t worry, your veterinarian can take a small piece of the ligament, and your horse will still be able to hold up his head. For information on this, have your veterinarian contact:
Dr. Jaroslava Halper, Department of Pathology
College of Veterinary Medicine, The University of Georgia
Athens, GA 30602-7388
Now for the really bad news; there is currently no cure for DSLD. Of course, the lack of a cure should stop absolutely no one from trying to find a cure, and it doesn’t even stop a few people from claiming that they do have a cure. Internet support groups have formed, and various treatments have been proposed, but nothing has really been shown to slow down the disease – and certainly not cure it – in good studies (trust me, if there was anything that really worked to cure a horse of DSLD, everyone would be using it).
The typical treatment for a DSLD horse is based on things that people think that the ought to do, such as “supporting” the limb by means of various shoeing and bandaging techniques, reduction in exercise, and pain relievers, as needed. More novel therapies, and various supplements, have also been proposed. Unfortunately, ultimately no treatment has been shown to be effective in stopping disease progression (and since you don’t know how the disease will progress in any one horse, it’s hard to say how it might have done without the treatment that you think is working).
The best way to deal with DSLD is to try to avoid it. If you’re purchasing a horse from an affected breed, it wouldn’t be a bad idea to look into its genetic history (if possible). Ultimately, selective breeding and identification of affected strains – as has occurred with HYPP – will be needed to eliminate this problem.