Photo 1: A moderate to severe case of chronic progressive lymphedema, with swelling of the leg and formation of pastern folds
and numerous skin nodules that are eroded. (PHOTOS: COURTESY OF DR. VERENA AFFOLTER)
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It's a painful, disfiguring disease that may strike horses as early as 2 years of age, then over time cause formation of large
nodules that interfere with normal pastern movement, permanent skin ulceration and lameness, eventually leading to the animals'
early demise.
The disease is chronic progressive lymphedema (CPL), and it affects large draft breeds with heavily feathered lower extremities.
Early on, the disease may appear to be what often is referred to as a therapy-resistant pastern dermatitis, "scratches" or
"mud fever," but over time, in addition to skin lesions typical for scratches, affected horses have vascular and lymphatic-vessel
changes.
That was found during skin-lesion biopsies submitted to the dermato-pathology service at the University of California-Davis,
as reported by Verena Affolter, DVM, PhD, Dipl. ACVP, a professor of dermatopathology, Department of Pathology, Microbiology
and Immunology at UC-Davis' School of Veterinary Medicine, in "The Horse Report," published by the school's Center for Equine
Health (Vol. 19, No. 4, October 2001).
Photo 2: This is a more severe form of CPL with marked swelling and oozing of the skin surface. The partially regrown feathering
is covering some of the nodules.
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"The progressive disease is characterized by progressive swelling, fibrosis, marked hyperkeratosis and formation of skin nodules
of the distal limbs," says Hilde DeCock, DVM, formerly Affolter's colleague in the same department and now working and teaching
in Belgium.
The disease is seen in primarily in Shires, Clydesdales and Belgian draft horses, while other draft breeds are not affected,
and certain genetic lines are more readily prone to develop clinical signs, indicating at least a partial genetic etiology
and a hereditary component, the colleagues explain.
Although CPL is seen around the country and the world in the three draft breeds, only the researchers at UC-Davis and their
colleagues in Ghent, Belgium, are conducting ongoing studies.
They are exploring the genetics and control of the disease, seeking a definitive cause and a method to successfully manage
afflicted horses.
Photo 3: The skin surface has marked hyperkeratosis and the epidermis is markedly thickened, Secondary infections are common,
as shown here with an inflammation of the hair-follicle opening.
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The genetic studies include evaluation of the elastin gene, which is currently studied in Leuven, Belgium, and the vascular
endothelial growth factor receptor 3 (VEGFR-3), which is studied at UC-Davis by Danika L. Bannasch, DVM, PhD, associate professor
in genetics, Department of Population Health and Reproduction. The FOXC2-gene, associated with distichiasis and lymphedema
in humans, was evaluated by Bannasch and found to not be associated with equine CPL.
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