Degenerative suspensory ligament desmitis (DSLD) is a progressive and devastating lameness that’s gaining attention.
In this condition, there is failure of normal healing, with the ligament in involved legs becoming progressively thicker and more spongy. Once thought to be a problem only of the suspensories, recent research has discovered this is actually a bodywide problem.
Onset is often in early adulthood. The earliest symptoms are often vague and nonspecific, such as unexplained stumbling and vague lameness that may shift from leg to leg (see our table for symptoms of ligament/tendon injury vs. DSLD).
Stiffness, especially when rising, is common. It’s not unusual for a DSLD horse to have a long history of lameness and neurological exams and to be misdiagnosed in these early stages. The horse may have asymptomatic periods interspersed with times when symptoms are again obvious. As the disease progresses, changes in the fetlocks become obvious. It may strike the front legs first or the hind legs, may be worse in one leg but always involves more than one.
The first change is often swelling, followed by obvious thickening of the suspensory, usually in the suspensory branches. The joint pouches of the fetlock joint may be enlarged. Heat may be obvious. Palpation of the suspensories elicits a pain response and ankle flexion tests are positive, often extremely so and disproportionate to the amount of lameness the horse may be showing.
At this stage, there’s still a pattern of ”flares” of symptoms alternating with relatively good periods but over time the suspensories become progressively enlarged, painful and develop a mushy consistency on palpation when the leg is held up but may feel abnormally tight when it is bearing weight.
Conformation changes occur, with the fetlocks either dropping down and the horse becoming coon footed, or the opposite may occur, with the fetlocks becoming very upright. When a hind leg is involved, the whole limb may become post legged. Eventually, the condition progresses to the point that the horse is constantly in pain, may even go down and refuse to rise. Euthanasia is often the only option for these horses.
The gait changes with DSLD. Common abnormalities include toe first landing, development of a ”rope walking” like gait, traveling extremely wide behind when the hinds are involved, and hopping like a rabbit at the canter when the hinds are involved. These gait changes sometimes lead to a misdiagnosis of neurological disease. To relieve the strain on their ankles, DSLD horses often dig holes to stand in toe first. When the hind legs are involved, they may sit on fence lines or rocks to rest their legs and may be observed dog sitting.
In the early stages, behavior changes, especially reluctance to work, are common. DSLD horses often have episodes that look like colic/abdominal pain but nothing is found to explain it on examination. Areas other than the fetlocks, such as the back, patellar ligaments of the stifle, and hip joints are commonly painful.
In the later stages, many horses seem to age rapidly, with muscle wasting. Extremely stretchable skin, that may even hang loosely in wrinkles, develops in some cases. Some horses develop hard, boxy swellings along the sides and back of their hocks. Flexor tendons may slip out of position at the point of the hock. Many owners report their DSLD horses develop allergies for the first time in their life, and mares frequently abort. Whether these last two are directly linked to the disorder, or secondary problems caused by stress, has not been determined.
Careful and thorough postmortem examinations performed by Dr. Jaroslava Halper, from the Veterinary School at the University of Georgia, found that the same abnormalities seen in suspensories from DSLD horses can also be found in the flexor tendons, patellar tendons of the stifle, the nuchal ligament in the neck, arteries and the sclera (”whites”) of the eyes. This study confirms that DSLD is a systemic, body-wide disease, not a local problem with the suspensory ligaments. Dr. Halper also had the opportunity to study a skin biopsy from a DSLD horse with the loose skin symptom and reported there was almost complete absence of elastic fibers in the skin.
Until recently, the only way to definitively diagnose DSLD was by postmortem examination of the legs. However, with the finding that the nuchal ligament shows the same changes as the legs, nuchal ligament biopsy has emerged as a possible definitive test that can be done on the live horse. Anyone interested in information on this test should contact Dr. Halper by calling 706-542-5830 or contact her by e-mail through her web page at http://www.vet.uga.edu/vpp/halper/halper.html.
Otherwise, a presumptive diagnosis is made by history combined with physical examination, response to flexion tests and ultrasound appearance of the suspensory ligaments. One odd characteristic of DSLD is that the ligaments will begin to enlarge before they show ultrasound evidence of ”holes” and disrupted fiber patterns that most vets will be looking for to confirm a diseased tendon or ligament. For this reason, measurement of the size/thickness of the suspensory body and suspensory branches is also important.
Dr. Jeannette Mero has been studying DSLD for a number of years, and in 2000 founded the nonprofit organization DSLD Research Inc.
Dr. Mero has put together an examination and ultrasound protocol for DSLD, with detailed guidelines related to where along its length the suspensory should be measured, in what planes to measure and suggested cut offs for normal suspensories.
The hallmark of DSLD compared to other tendon/ligament problems is the progressive enlargement of the ligament over time. Dr. Mero’s protocols and examination forms can be found at http://www.dsld.org/, as well as sample ultrasound images from DSLD horses and some photos of postmortem specimens. Dr. Mero’s phone number is 209-966-3964, and she said she is available for consultations.
The long-term prognosis for a horse with DSLD is extremely poor. Although there can be long periods where the degeneration seems to stabilize and the horse is reasonably comfortable, this is a progressive condition that will usually end up with euthanasia. While opinions differ on riding DSLD horses during their relatively asymptomatic periods, a rider’s weight is extra burden on the weak legs. Mares should not be bred, both because of the likely genetic component and because the weight of the pregnant uterus is a severe strain on them.
Some specialized shoeing techniques have been developed and been successful in stabilizing the disease for prolonged periods of time in some non-Peruvian horses but do not work well for the Peruvians horses.
Most owners are having the best results with keeping their horses barefoot, with frequent attention to keeping the feet meticulously balanced and the toes well backed up. These horses also typically do best when kept on as much turnout as possible.
Some people find sports boots or support wraps help their horses be more comfortable. NSAIDs are typically used when horses are having a flare, as well as the usual intensive cooling/icing and wrapping to control swelling. Some horses are maintained on MSM and/or devil’s claw.
Preliminary results with a new treatment are showing promise. Research in people with degenerative ligament and tendon injuries found excellent pain relief and improved clinical outcomes when they were treated with a topical nitric oxide, either nitroglycerin or isosorbide compounds.
The healing process in normal tendons is highly dependent on production of nitric oxide at all stages of healing and absence of nitric oxide leads to exaggerated inflammatory responses.
Because of this, a trial is underway following the response of DSLD horses to supplementation with Jiaogulan and a nutritional supplement that supplies the raw nutrients needed for the body to manufacture nitric oxide. So far, reports have been positive, with reductions in pain, sometimes quite dramatic, being seen in the same time frame as in laminitic horses treated with Jiaogulan, within one to three days.
Reductions in swelling and abnormal consistency to the ligaments have been documented, less heat or resolution of heat when it was present, more freedom in the gait and even loss of the very wide way of moving behind and ”bunny hopping” canter in two horses.
Anyone interested in more information on this trial should join the group http://groups.yahoo.com/group/DSLD-equine/. Membership is free. Dr. Eleanor Kellon, our veterinary editor, is overseeing this trial.
Although there’s still a lot left to be learned about DSLD, understanding is growing. The nuchal ligament biopsy and ongoing genetic studies will enable DSLD to be diagnosed with certainty much earlier and prevent breeding of affected horses. The hope is that investigation into environmental risk or confounding factors, and trials of novel treatments, will help make horses more comfortable.