Chronic progressive lymphedema in Belgian draft horses

Photo: Brent Coulter/Adobe Stock

The Belgian draft horse is a culturally significant breed in Belgian agriculture. It is currently threatened by high levels of inbreeding that are impacting the breed’s health.

Belgian draft horses are vulnerable to chronic progressive lymphedema (CPL), an incurable condition with approximately 86% of Belgian draft horses affected. Other draft breeds are also at high risk for the condition. In a disease review published in the journal Veterinary Sciences, the authors describe 2 possible hypotheses for CPL pathogenesis and report recent advances in the management of the condition, including a newly developed scoring system for clinical severity.

CPL is characterized by increasing swelling on the distal portion of the legs, scaled dermal fibrosis, and the development of skin folds and lesions. The physical state of the skin folds significantly increases the risk of secondary bacterial and parasitic infections, further burdening the animal. CPL causes significant morbidity and often requires premature euthanasia due to its severity.

The condition’s etiology and pathogenesis remain unclear. The authors review 2 main hypotheses that have been reported to describe how CPL begins, but both include lymphatic involvement, fibrosis, inflammation, and unnatural elastin dynamics. The order of events drives the differences between the 2 hypotheses. Does lymphedema cause inflammation and fibrosis or does chronic inflammation and fibrosis result in disruption of the lymphatic system? Or do each of these factors reinforce each other, creating a cyclic perpetuation of complications? Additionally, genetic involvement could cause elastin failure or autoimmune related inflammation.

The first hypothesis suggests that the lymphatic system fails to drain due to inadequate elastin support and function specifically in dermal tissue. Elastin is necessary to support lymphatic vessel connections. This idea is supported by significantly lower measured levels of dermal elastin in susceptible horses compared to those from non-susceptible breeds and the presence of anti-elastin autoantibodies in affected horses. Lymph build-up would then lead to fibrosis, skin folding, and nodule formation.

The second hypothesis proposes that chronic inflammation results in tissue edema and lesion formation. Fibrosis and hyperkeratosis would result from inflammation and in turn cause lymphatic blockage. Although the inflammation could be secondary to infection, vasculitis, or chemical irritant, the hypothesis also includes that autoimmune responses may be to blame. This hypothesis is supported by genetic association of overregulated autoimmune regions with CPL-associated regions.

The authors also report data on the factors associated with the occurrence and severity of CPL. Increased age, stallions, secondary infections, housing environment, use of the animal, diet, and distal limb conformation all have been associated with increased occurrence and severity of CPL. To improve owner and veterinary communication of this serious condition, the authors developed an updated grading system that incorporates a pictorial representation of impacted tissue presence and distribution.

Clara Bechtold is a 2024 PharmD candidate, studying veterinary pharmacy, at the University of Connecticut in Storrs.

Reference

Brys M, Claerebout E, Chiers K. Chronic progressive lymphedema in Belgian draft horses: understanding and managing a challenging disease. Vet Sci. 2023;10(5):347. doi:10.3390/vetsci10050347