and wet conditions, this situation should be modified to allow more time in dry paddocks or clean stalls. Many topical treatments have typically been tried in these cases, thus it is not uncommon for many patients to have also developed a contact dermatitis. It is therefore important to only use topical therapy that is needed and minimize the unnecessary use of topical products that may be irritating. If contact allergy to plants or shavings is suspected, confinement can be done as part of the diagnostic plan. This can be done by applying bandages to the area after thorough cleaning of the skin or changing the life style of the animal for 7-10 days (if no infection is present). For example, if the horse is on pasture, it can be stalled and only turned out in a round pen where there is no grass. If the animal is primarily in a stall with shavings, either a different type of shavings can be used or turn-out can be done to rule out contact allergy. If a case has contact allergy and completely resolves with confinement, re-challenge will lead to recurrence of the lesions within 24-48 hours after exposure. Contact allergy is best managed with avoidance. If this is not feasible, then protective gear, as well as oral pentoxifylline, can be implemented. Pentoxifylline is dosed at 10mg/kg 3 times daily. If infections have been treated, the next step can be to biopsy for histopathology to identify the underlying disease. Vasculitis can be a cause of pastern dermatitis. This can be triggered by a variety of antigens or it can be idiopathic. Effort should be placed in the identification of the triggering cause, if at all possible. Careful review of drugs, de-wormers and vaccinations should be done. Food trials can also be considered in the event that the suspected trigger is an ingredient in the horse’s diet. Pentoxifylline is also the drug of choice for vasculitis. This drug is safe for long-term use and is typically well tolerated. Topical glucocorticoid therapy is also frequently used to decrease inflammation. The use of systemic glucocorticoids is reserved for severe cases that are not responsive to other treatments. The potential for inducing laminitis should be considered before prescribing this form of therapy. It is also important to avoid insect exposure as some species of Culicoides preferentially affect the lower legs of horses. Use of repellents such as 2% permethrin should be done daily in areas of greatest exposure. In some draft horses (Shire, Clydesdale, and Belgian draft horses), a genetically inherited2 immune dysregulation leads to vasculitis and chronic progressive lymphedema. This condition is characterized by progressive swelling, hyperkeratosis and fibrosis of the distal limbs. This condition is thought to have a genetic component and is chronic-progressive3. The disease starts at an early age, progresses throughout the life of the horse, and often ends in disfigurement and disability of the limbs. Antibodies against elastin have been detected in affected horses.4 Horses with clinical signs of chronic progressive www.faep.net
lymphedema have been found to have significantly higher anti-elastin antibody levels compared to clinically normal Belgian Draught horses and to healthy Warmblood horses. These levels correlate with the severity of the lesions. These antibodies could be used for early diagnosis of this condition and possibly to help with breeding programs to limit the breeding of individuals prone to this disease. In summary, may different diseases can manifest as pastern dermatitis. Due to numerous possible underlying causes, a systematic and logical approach is crucial. History, careful physical exam and identification of primary lesions (when still present) are important in aiding the clinician to formulate the best diagnostic plan for each individual case. In most cases, secondary infections are present and complicate the evaluations; thus successful identification of the underlying disease will also depend on complete resolution of the secondary infections. References
1. Rüfenacht S, Roosje PJ, Sager H, Doherr MG, Straub R, Goldinger-Müller
P, Gerber V. Combined moxidectin and environmental therapy do not eliminate Chorioptes bovis infestation in heavily feathered horses. Vet Dermatol. 2011 Feb;22(1):17-23. 2. Mittmann EH, Mömke S, Distl O.Whole-genome scan identifies quantitative trait loci for chronic pastern dermatitis in German draft horses. Mamm Genome. 2010 Feb;21(1-2):95-103. 3. De Cock HE, Affolter VK, Wisner ER, Ferraro GL, MacLachlan NJ. Progressive swelling, hyperkeratosis, and fibrosis of distal limbs in Clydesdales, Shires, and Belgian draft horses, suggestive of primary lymphedema. Lymphat Res Biol. 2003;1(3):191-9. 4. van Brantegem L, de Cock HE, Affolter VK, Duchateau L, Hoogewijs MK, Govaere J, Ferraro GL, Ducatelle R. Antibodies to elastin peptides in sera of Belgian Draught horses with chronic progressive lymphoedema. Equine Vet J. 2007;39(5):418-21.
Rosanna Marsella, DVM, DACVD Dr. Marsella is a graduate of the University of Milano (Italy, 1991). After graduation, Dr. Marsella worked in private practice for a couple of years and then decided to pursue specialty training in dermatology. She became a board certified dermatologist in 1996, and soon after accepted a faculty position at Virginia Tech University. In 1997 she returned to Florida to join the faculty of the University of Florida, where she is a full Professor. Her special area of research interest is allergies and identification of new therapies. Dr. Marsella is a horse lover and owner, and has a special interest in equine dermatology.
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