Lymphangitis

Frankly, I hate this disease. In a nutshell, a limb (usually one hind limb) will become infected with bacteria that normally inhabit the skin through a wound that may be unseen by even the most astute caregiver. Moreover, the injury may have come and gone before this disease appears.

The first sign of lymphangitis is a small localized swelling on the limb. It is often overlooked or regarded as a “bruising” caused by trauma. This swelling becomes larger with heat and pain as the infection takes hold within a day. Soon the swelling runs from the hoof up to the stifle (or the equivalent in the forelimb), with serum oozing through the skin, forming small hard beads of dried serum.

In reading any discussion on lymphangitis, there are a few common points:

  • First, the cause is an inability of the horse to mount an appropriate immune response against a bacteria or fungus within the leg.
  • The infection and the aggressive immune response damage the lymphatics, which are responsible for draining the fluids and the limb’s debris.
  • The blood continues to enter the limb and perfuse into the tissue under pressure but cannot leave, causing intense swelling like an overfilled balloon with water. This stagnant blood is a breeding ground for invading bacteria.
  • There are several causal agents, but Staphylococcus, Streptococcus, mixed skin, and environmental bacteria are common.
  • It can become chronic with a lifetime of recurring painful swelling, even with being aggressively treated.

I have always aggressively treated any lower leg injury and lower limb swelling, even with no visible cut. Apply a pressure wrap and keep it on when stabled helps to press any excess fluid into the circulation. I also apply cold water therapy under pressure (cold water from a hose, hydrotherapy). I clean the whole limb using Betadine Scrub washing daily, followed by a clean pressure wrap applied to the dried leg. Antibiotics work well only if there is no swelling because most antibiotics cannot penetrate edema.

Cleanliness, pressure wraps and exercise are critical in the early stages. Once the edema becomes hot and painful, indicating a bacterial infection, treatment success becomes less effective. As time goes on and the lymphangitis recurs, the only solution is to pressure wrap, exercise and give medical treatment as your vet prescribes. These may be an antibiotic (hopefully cultured for an effective one), a systemic steroid or both.

Infections, by rule, cause the immune system to respond with various weapons to fight the disease. With the COVID pandemic, we have heard much about the immune system. As with COVID, the damage often occurs from an overactive response from the immune system. Other bad immune reactions that attack the body’s tissues are called autoimmune reactions. I suspect that some of these horses with lymphangitis have another factor triggered when the insult initially occurs. However, according to resources, no other conditions are associated with these cases, including breed, age or gender. Sometimes it happens in only one horse on a farm of many horses, and occasionally several horses on a farm are affected. We just haven’t been able to (or there is no money for research) discover the exact pathogenesis of lymphangitis.

My heart goes out to owners with horses suffering or lost to lymphangitis. One of the moments that drove me to become a veterinarian was when a horse I was placed in charge of had lymphangitis of one hind limb. The skin and tissue of this horse were destroyed in the cannon area, revealing the underlying tendons causing her euthanasia. The smell is present in my mind as I write this.

The lesson here is to treat every leg swelling as if there is a cut that can become infected. Try to reduce systemic inflammation through diet, environment and social changes – I write about this elsewhere.

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