Degenerative Ligament Disease Reaches Beyond the Limbs
Horse Health Press Release
Researchers at the University of Georgia (UGA) College of Veterinary Medicine have discovered that degenerative suspensory ligament desmitis (DSLD), a common disorder in horses once thought to involve only ligaments in the legs, actually affects connective tissue throughout the body.
As a result of the finding, lead author Jaroslava Halper, MD, PhD, and her colleagues recommend that DSLD be renamed to reflect more accurately the disorder's true nature.
"It's a systemic disorder involving accumulation of proteoglycans (a class of molecules that help organize connective tissue so that it is elastic yet strong)," said Halper, an associate professor of pathology. "So we propose equine systemic proteoglycan accumulation, or ESPA, as a more appropriate name for the condition."
The disorder affects an estimated 1 percent to 7 percent of horses, and it's most commonly detected in Peruvian Pasos. It also affects Arabians, American Saddlebreds, American Quarter Horses, Thoroughbreds, and some European breeds. Affected horses become lame as the lower portion of the leg swells. There is no cure, so horses with advanced cases of the disorder are often euthanatized.
"The impact of this disease is huge," said co-author P.O. Eric Mueller, DVM, PhD, Dipl. ACVS, professor of surgery and chief of staff at the UGA Large Animal Veterinary Teaching Hospital. "These are young horses that should be at the pinnacle of their performance that start to drop at the fetlock and show lameness."
Halper said the first clue that DSLD/ESPA was a systemic disorder was the anecdotal evidence that horses with the disorder--which tends to run in families--are known to suddenly develop fatal aortic ruptures. Similarly, people with Marfan syndrome, an inherited disorder of the connective tissue, are prone to sudden death from aortic ruptures.
She also had trouble believing that only the suspensory ligament of the lower leg would be affected by the disorder. She reasoned that a horse is likely to have trouble walking if its weight-bearing suspensory ligament is damaged, but connective tissue elsewhere in the body could also be diseased without a horse altering its behavior.
"It just didn't make any sense to me that the disorder would be localized to the suspensory ligament," Halper said. "So I started to look at other tendons and ligaments."
Halper and her colleagues examined tissues and organs from 28 horses with the disorder and from a control group of eight horses that did not have the disorder. When viewed under a microscope, tissues from other ligaments in the body as well as vessels and organs with significant amounts of connective tissue, such as the aorta, appeared diseased. Specifically, the tissue had an accumulation of proteoglycans.
The finding has made the researchers' results, published in the journal BMC Veterinary Research, the third most widely read article in the journal's two-year history. The article was published in April and was the most frequently read article for three months.
The finding has also led the researchers to study a new diagnostic test for the disorder. By examining a thin sliver of tissue--about the size of a human fingernail--from the large ligament on the back of a horse's neck under a microscope, veterinarians can detect the excess proteoglycan accumulation before a horse starts displaying clinical signs.
Because the disorder tends to run in families, horse owners can choose not to breed predisposed horses. Owners can also manage predisposed horses so that they place less stress on the weight-bearing ligaments of the legs to potentially reduce the likelihood of lameness.
"Now we have a relatively simple, safe technique that can identify predisposed horses," Mueller said. "As we do this work and link it to genetic studies, we can ultimately minimize the incidence of the disease through selective breeding."