Chronic Progressive Lymphoedema

Chronic Progressive Lymphoedema or CPL is a lifelong disease that affects draft horses with feather. There is no cure. It is noted in Belgian drafts/Brabants at an estimated 96% prevalence and is becoming increasingly common in other breeds:- Shires, Clydesdales, gypsy vanners, cobs, Percheron, Boulonnais and Friesians are all affected. Some correlations have been noted between the incidence of CPL and bone and hair thickness.

Essentially CPL is a failing of the lymphatics in the lower legs. We know in part this is caused by the fact that equines don’t have muscles below the knee and hock that contract against the lymph vessels to aid the flow of lymph. Therefore they rely on the movement of the fetlock joint and natural hoof function instead of muscular contraction, making them very prone to lymphatic incompetence when standing still. This is why horses that are stabled are far more likely to develop CPL – when standing still for long periods the natural lymphatic retraction is removed.

Researchers suspect that CPL is a complex disease consisting of a multifactorial process involving an underlying genetic cause and triggers from the horse’s environment and husbandry. There seem to be differences in the sexes – stallions can develop CPL later but more severely compared to mares who develop it earlier. The exact gene or mutation is yet to be identified. In one study horses with CPL were shown to lack a protein called elastin which normally acts as a sort of compression bandage to stimulate the lymph back into circulation. Indeed several studies have noted altered elastin metabolism in CPL horses. This elastic squeezing action is what is replicated in lymphoedema care by way of Combined Decongestive Therapy.

The trapped waste and fluid (lymphoedema) causes the body to produce fibrotic and adipose tissue. It also creates inflammation which causes the blood capillaries to open up so more lymph is produced. This is why mites and bacterial infections causing inflammation also logically worsen the oedema. This fibrotic, adipose tissue is what makes up the skin folds and nodules that are so unique to the disease. It is important to note that lymph can not travel through fibrotic (scar) tissue deeper than 4mm.

CPL is frequently misdiagnosed as feather mites, “cob legs” and mud fever/greasy heel. It is reliably diagnosed from physical presentation and can be further investigated and monitored using the Press and Stretch Test, developed by Rebecka Blenntoft.
These horses are also prone to chronic thrush which can be treatment-resistant and can develop laminitis.

It is important to note that feathered horses, especially with CPL, are prone to hyperkeratosis (an over-production of keratin) which causes skin crusts on which feather mites feed. Left untreated these mites can cause scarring and damage to the delicate tissue and superficial lymph vessels and as such must be recognised as one of the major triggers of CPL.

“C.bovis infestation may affect the progression of chronic pastern dermatitis (also known as chronic proliferative pastern dermatitis, chronic progressive lymphoedema and dermatitis verrucosa) in draft horses, manifesting with oedema, lichenification and excessive skin folds that can progress to verruciform lesions.”

Silvia Rüfenacht Petra J. Roosje Heinz Sager Marcus G. Doherr Reto Straub Pamela Goldinger‐Müller Vincent Gerber

In yellow is a crease caused by hyperkeratosis. It is essentially “mallenders“, just further down the leg. Once the area has been allowed to scar like that it can create problems for the superficial drainage as the lymph can not pass through scar tissue thicker than 4mm.

Creasing like this can be prevented to some degree by applying an emollient regularly and using something like Sebolytic® shampoo to remove the keratin build up and restore the natural balance of the skin.