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CHRONIC PROGRESSIVE SWELLING, HYPERKERATOSIS AND FIBROSIS OF DISTAL LIMBS IN CLYDESDALES, SHIRES AND BELGIANS SUGGESTIVE OF CHRONIC LYMPHEDEMA. A
condition characterized by progressive swelling, hyperkeratosis and fibrosis
of distal limbs has been recognized in Shires, Clydesdales and Belgian
Draft horses. This chronic progressive disease starts at an early age,
progresses throughout the life of the horse and often ends in disfigurement
and disability of the limbs which inevitably leads to the horse’s
premature death. The pathologic changes and clinical signs closely resemble
a condition known in humans as chronic lymphedema or elephantiasis nostras
verrucosa. The lower leg swelling is caused by abnormal functioning of
the lymphatic system in the skin, which results in chronic lymphedema
(swelling), fibrosis, a compromised immune system and subsequent secondary
infections of the skin. Based on preliminary research, it appears that
a similar pathogenic mechanism is involved in the disease that affects
these specific draft horse breeds. The clinical signs of this disease
are highly variable. The earliest lesions are characterized by skin thickening
and crusting; both are often visible only after clipping the long feathering.
Secondary infections develop very easily in these horse's legs and usually
consist of either chorioptic mange or bacterial infections. Both dark
and white skin on the lower legs are equally affected. These lesions are
consistent with pastern dermatitis, a process also seen in other breeds.
In Shires, Clydesdales and Belgians however, these lesions do not respond
well to therapy. As the condition becomes more chronic, the lower leg
enlargement becomes permanent and the swelling is firm on palpation. More
thick skin folds and large, poorly defined, firm nodules develop. The
nodules may become quite large and often are described as "golf ball"
or even "baseball" in size. Both skin folds and nodules first
develop in the back of the pastern area. With progression, they may extend
and encircle the entire lower leg. The nodules become a mechanical problem
because they interfere with free movement and frequently are injured during
exercise. This disease often progresses to include massive secondary infections
that produce copious amounts of foul-smelling exudates, generalized illness,
debilitation and even death.
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