Owners of draught (draft) breeds have long experienced a disease of the pasterns that at first resembles scratches but does not respond to treatment and progresses to a debilitating nodular skin disease of the horse. The cause has remained unknown but there does seem to be a genetic component as the disease is confined to certain breeds. The disease has been termed Chronic Progressive Lympoedema (CPL) as recent studies have found that the cause of the swelling and node formation are defects in the lymphatic system. In this article we address how this occurs, treatments, and prognosis.

The condition is characterized by a progressive swelling, thickening of the skin (hyperkeratosis), and formation of large nodules (fibrosis) of the lower portions of the limbs in Shire, Clydesdale, and Belgian draft horses. With time, secondary infections and ulceration occur. The disease starts at an early age, progresses throughout the life of the horse, and often ends in disfigurement and disability of the limbs that inevitably leads to the horse's premature death.

Scoring system for CPL-associated lower-limb lesions in draft horses.

Severity	Score	Swelling and deformation	Skin surface and hairs
Normal	0	Normal limb diameter	Hairs are supple
Mild: Below fetlock	1	Normal limb diameter, Soft, compressible swelling, 1–2 SF (P/PL)	Slight skin thickening, Hyperkeratosis, Hairs supple, (Hock: hairs upright)
Moderate: Until fetlock	2	Normal limb diameter, Moderate hard, diffuse swelling, > 2 SF and NOD (D/P/PL)	Moderate skin thickening Hyperkeratosis Small wounds, ulcers Hairs less supple (Hock: hairs upright + exudate)
Severe: Above fetlock	3	Increased limb diameter Hard, diffuse swelling SF and NOD (D/P/PL) Mechanical impairment	Severe skin thickening Hyperkeratosis Several wounds, ulcers, exudate Greasy skin + bad odor Hairs rough + broken Hock: hairs upright + exudate + wounds
Extreme: Above fetlock	4	Increased limb diameter Hard, diffuse swelling SF and NOD surrounding limb Severe mechanical impairment General loss of condition ‘Final stage’	Very severe skin thickening Hyperkeratosis Numerous wounds, ulcers, blood, exudate Greasy skin + bad odor Hairs rough + broken Hock: hairs upright + excessive exudate + large open wounds
SF = skinfolds, NOD = nodules, D = dorsal, P = palmar, PL = plantar. Adapted from De Keyser, K., Janssens, S., Peeters, L.M., Gasthuys, F., Oosterlinck, M., Buys, N., 2014. Chronic progressive lymphedema in the Belgian draft horse in Belgium: clinical phenotyping, prevalence and risk factor analysis. Vlaams Diergeneeskd. Tijdschr. 83(3), 119–124.