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DIAGNOSTIC PROTOCOL FOR DEGENERATIVE SUSPENSORY LIGAMENT DESMITIS (DSLD)
Revised February 2002

1. In early stages lameness is often not apparent. Even in advanced cases due to the bilateral nature of the disease lameness is not always obvious on baseline. Front limb afflictions look stiff, and are reluctant to move out and extend, tight circles will exacerbate the signs and may produce lameness. Hind limb affected horses move stiffly, will not drive in the rear, and will move with a widening of their gait. Peruvian horses normally gait close in the rear, with correct movement only having 1-2 hands width between the hocks and lower limbs. As the condition advances overt lameness can become apparent - however like arthritis cases, DSLD horses often after light exercise will appear to "work out of it" and move more sound.

2. Other common signs in early to mid stage cases include: changes in attitude, sourness about working, and signs
that suggest back pain. As the condition progresses horses will become increasing more reluctant to move about,
and will preferentially land with their toes first, particularly if the rear is affected. Eventually they will lay down more, and dig holes to stand in to relieve pressure - usually off of their rear limbs.

3. In very early cases, there are often no abnormalities noted on palpation. Investigate the suspensory ligament branches first - over 90% of all DSLD cases start here. Even in advanced cases the bulk of all histopath changes occur in the branches. DSLD is often missed because the body of the suspensory ligament appears normal and the branches are not investigated fully. Recent work has indicated that the majority of cases start in the lateral branches of the front limbs and in the medial branches of the rear limbs. Pain is usually the first abnormal palpation finding, often only mild manipulation of the branches will elicit a grunt and a pulling away of the limb. In mid to late stages a palpable thickening and hardening of the branches, and less commonly of the body of the suspensory ligament, occurs.

4. Tendon sheath and/or fetlock joint effusion may or may not be present. THIS IS NOT A GOOD DIAGNOSTIC INDICATOR. Some of the worst cases (all 4 limbs affected) on record had no wind puffs or joint effusion at all.
Some cases do have severe tendon sheath swellings, occasionally making palpation of the SL branches difficult.

5. Fetlock flexion tests are almost always positive on affected limbs and in some cases the horse is almost crippled
with a 5/5 response for several minutes. Early onset cases may show only a mild positive response 1-2/5. Fetlock flexion tests, along with palpation findings are the most useful physical exam signs in at least mid stage cases, as again lameness is not always apparent on baseline due to the bilateral nature of the disease.

6. The classic conformational signs of dropped fetlocks, coon shaped hooves, and straight hocks and stifles while common, do not always occur. These signs are only noted in mid to late stage horses and when they are seen they are almost always indicative of DSLD. However, again some of the worst cases of DSLD noted had fetlocks that never dropped below the horizontal.

7. Sonographic exam is needed to positively diagnose the disease antemortem. Look in the SL branches first. Do not look for overt tears or hypoechoic lesions per se. Do a full sonographic exam of all areas of the SL, however zones 3 A/B in the front limbs and 3B/4A in the rear limbs, or just proximal to the fetlock joint, with a cross-sectional view, has proven to be the site that yields the most results. Scanning the SL branches individually on cross section at the level of the fetlock joint is also useful. In early stages only a thickening of the branches as noted by an increase in the whitening or a hyperechoic appearance may be noticed. As the disease continues the branches become enlarged, and continue to thicken. Normal SL branches are at their largest 1cm to at most 1.2cm or less, the SL body can range up to 2cm just below the knee or hock. In DSLD horses the branches continue to enlargen over time, in advanced cases the branches in the zones noted above seem to jump out and fill up the distal screen of the ultrasound machine. The worst case so far has been documented with a rear lateral suspensory branch at 4cm and was bright, bright white.

Less commonly will overt lesions as noted by dark holes, or hypoechoic lesions, be seen. This is again a common
reason for a misdiagnosis or even a DSLD horse to be called normal on a scan, because less than 30% of cases have actual tears or lesions. Dark lesions are usually only noted in severe and advanced cases and are not useful, consistent findings in early onset cases. Less commonly will the SL body be involved but usually with similar signs as found in the branches. Poor fiber pattern may be noted on longitudinal scanning in either the SL body or branches.

8. This is a bilateral or quadrilateral disease, but in early cases often only one leg may be noted, or one limb may be more affected than the contralateral limb at any given time. Horses that are affected in all four limbs are markedly more painful and deteriorate faster. Often hind limb only affected horses can remain pasture comfortable for many months to years. Generally this is a slowly progressive, insidious disease with most cases going months to years in the early stages before diagnosis. Average age of onset is between 4 and 10 years, with the range being from weanlings to 20 years of age.