Equine Pastern Vasculitis Still Puzzling Researchers

Equine Pastern Vasculitis Still Puzzling Researchers

Researchers still don't know exactly what causes pastern vasculitis, but possible causes include a specific plant touching the pastern, specific medications, a reaction pattern specific to the horse, or several triggers.

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There's not much good news on the pastern vasculitis front: Despite intense research, scientists still have not been able to uncover anything reassuring about the condition--no common cause, no successful treatments, no positive prognoses.

“Our study cannot contribute to a more positive prognosis (for the disease),” said Monika M. Welle, DrMedVet, PhD, Dipl. ECVP, of the Institute of Animal Pathology at the University of Bern's Vetsuisse Faculty, Switzerland. “We were hoping to find the causative agent or a treatment option for this disease but did not find any. However, now we at least can say that none of the treatment options used so far is successful, and thus the veterinarian can give a prognosis based on a study.”

Pastern vasculitis—a different problem than pastern dermatitis, or scratches—causes swelling, redness, and raw and/or crusty skin lesions in the pastern area, but lesions can extend to the cannon bone, Welle said. It appears to be an immune-related problem characterized by inflamed blood vessels as seen in hypersensitivity reactions, she said; the damage to the blood vessel walls causes the clinical lesions.

Welle and colleagues investigated biopsies from the affected skin of 20 horses with a confirmed pastern vasculitis diagnosis and compared them to biopsies from 10 healthy horses. They sought to find an underlying cause, make a connection between microscopic findings and outcome, and evaluate treatment efficacy.

Unfortunately, the researchers were unable to determine any specific underlying causes, the histological findings in the skin biopsies were not related to disease development or progression, and, generally speaking, treatment of all kinds was ineffective.

“The type of vessel lesions suggests that there may be a hypersensitivity reaction against a causative agent that we haven’t identified yet.” Welle said. “It may well be possible that a certain drug, such as a deworming medication, or a specific plant on the pastern could be the trigger. But the vasculitis may also be a reaction pattern of the horse and may be caused by several triggers.” A more extensive, specific study evaluating this precise question would be needed to answer that mystery, she added.

Despite these disappointments, the researchers were able to make one conclusion about prognosis: Their study results indicated that hind limb pastern vasculitis has a less positive outcome than forelimb pastern vasculitis.

Although the condition appears to be related to hypersensitivity, this does not make it an “allergy” per se, Welle said. Furthermore, she noted, suggestions that white parts of the horse’s legs develop pastern vasculitis as a result of sunlight is probably inaccurate, as recent research does not support this theory.

“Pastern vasculitis is a serious disease that should be evaluated and treated early by an experienced veterinarian,” Welle said. Although in most cases treatment is not curative and the recurrence rate is high, treatment can help ease the discomfort affected horses experience, she added. In addition, changing the environment or medication the horse is receiving could possibly remove the potential causative agent, if there is one, she said.

The study, "Equine pastern vasculitis: a clinical and histopathological study," was published in the Veterinary Journal

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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