There are still so many things that baffle veterinarians and researchers, including how to manage chronic leg swelling called lymphedema that can lead to many more problems for the horse's health and comfort.
Lymphedema is a painful condition that occurs when the soft tissues retain fluid left behind after the cardiovascular system sends blood to the tissues and organs. Normally, the lymphatic system collects lymph (the remaining fluid) and returns it to the heart via a network of lymph vessels and lymph nodes. When something disrupts the lymphatic system's process, lymph collects in the appendages, thus causing swelling.
There are many causes of lymphedema in people, but the most common causes are surgical removal of the lymph nodes to treat cancer and infection. In horses, infection is by far the most common cause of lymphedema and is typically referred to as lymphangitis.
So, what is lymphangitis?
Lymph fluids are important to remove waste and toxins from the body's tissues.
Lymphangitis is often called different things: vasculitis, cellulitis, a staph infection or “big leg disease.” This horse disease is actually a recurrent bacterial infection. While it is identified by swollen legs, it is very different from a horse that is “stocked up.”
Stocking Up – non-painful swelling of the lower leg in two or more legs (typically the hind legs). Seen more as a minor issue, found in horses that have experienced a drastic decrease in exercise, perhaps due to an illness, weather or injury. It typically is resolved with light wrapping and upon return to exercise, even if it's just hand walking.
Lymphangitis – abrupt and intensely painful swelling of an entire single leg (again, typically a hind leg), accompanied by an elevated temperature (102-105 degrees F). The horse will exhibit more signs of discomfort and pain: depression, trembling, reluctance to move, rapid breathing, and sweating.
Lymphangitis is still a bit of a mystery in terms of how and why it occurs and ways to prevent it. The cause most often found is due to bacteria getting into the leg from a slight cut or abrasion. According to the AAEP, the bacteria then race to multiply:
“The bacteria reproduce quickly, causing inflammatory reactions of heat and swelling as the body attacks its invaders. The lymphatic system drains fluid from the leg, filtering it through lymph nodes that try to remove foreign pathogens (disease-causing organisms). The lymph nodes are overwhelmed and can, themselves, become infected. Lymph ducts and blood vessels become damaged and swollen and lose elasticity, with blood and lymph pooling on top of the one-way valves. The heart continues to pump fluid in, but the exits are blocked.”
The skin around the leg, which already lacks musculature, becomes tightly stretched as the leg swells, thus causing fluid seepage. That fluid can then burn the skin.
“Anything that can introduce bacteria under the skin and any sort of infection can lead to cellulitis and lymphangitis,” said Dr. Lauren Schnabel, professor of equine orthopedic surgery at North Carolina State University. “Wounds and insect bites can occur any time of the year in any climate, but moist humid environments are particularly a challenge. If there's any break in the normal skin barrier like happens with scratches, they'll be more likely to develop cellulitis and lymphangitis.”
Treatment for lymphangitis
Veterinarians will prescribe aggressive antibiotics and anti-inflammatories to combat the infection while also administering medication such as phenylbutazone and flunixin meglumine for the pain and swelling. While most swelling is tended to by cold therapy and bandaging, these treatments are often ineffective or only work for a short time before the swelling returns.
The biggest tool for treating lymphangitis is movement, which is difficult when the leg is so painful. So, what can be done?
In humans, the only way to encourage drainage for the lymphatic system is by lymphatic drainage massage. This type of gentle massage encourages the drainage of the lymph nodes and movement of the lymph fluids around the body. Humans can utilize lymphatic drainage massage, either manually or with a device, to move the fluid to be excreted from the arms and/or legs.
So how does this apply to horses?
Tune in next week to learn how a new treatment for lymphangitis might be the start of a revolution in horse healthcare.
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