Bacterial inflammation can cause tenacious condition lymphangitis

by Barbara Sheridan

AT SOME point, all horsemen have found one of their horses stiff and uncomfortable in its stall. Further examination has revealed a hind leg that is thick and swollen. This is not an uncommon sight, as horses seem to be a magnet for injuries that cause lameness. Legs always seem to be the focal point of injuries ranging from a kick by another horse to a self-inflicted mishap. However, before dismissing the condition as a minor injury that just needs bandaging and a few days' stall rest, think again. Something serious could be lurking beneath all that swelling, an infectious condition called lymphangitis.

A more serious sequel to swelling of the legs, lymphangitis is an inflammation of the lymph vessels usually caused by an infection entering into the body through an injury, such as a cut or wound. In the majority of cases, bacteria enter the lymph vessels through a wound in the lower leg.

Lymphangitis occurs when inflammation resulting from the bacterial infection rapidly spreads up the lymphatic vessels, obstructing the lymphatic flow and causing the vessels to swell and leak fluid from the inflamed tissues. The result is extreme swelling of the leg, which is why the condition is commonly called "big leg."

Not only is it difficult to diagnose, but it also can be difficult to treat.

The lymph system

When sickness or infection invades the body, the immune system is the first line of defense, which is supported by the lymph system. However, the lymph system that normally helps to keep the body healthy can cause its own set of problems.

"The lymph system contains a complex array of connecting low-

pressure vessels whose function is to carry excess fluid, inflammatory and immune cells toward lymph nodes and ultimately back into the systemic circulation," said Sharon J. Spier, D.V.M., Ph.D., professor of medicine and epidemiology at the University of California at Davis. "The lymph system serves to prevent a buildup of fluid in the limbs and alert the immune system to possible invaders, such as infection."

Should the immune system be unable to control the infection, the lymph system begins to back up, resulting in marked swelling, heat, pain, and lameness. Because of the location of lymph glands in horses, they are more prone to injury and inflammation in the limbs, causing lameness more often than other lymph-gland infections.

Noninfectious lymphangitis

Noninfectious lymphangitis often is seen in the heavy draft breeds. This disorder requires no treatment other than a purge of circulatory stimulants and walking exercise, with recovery achieved in two or three days.

Symptoms of noninfectious lymphangitis appear to be similar to the infectious form, and often one condition can be confused with the other. This sometimes results in the treatment of infectious lymphangitis being overlooked for several days until a proper diagnosis is obtained. The prognosis becomes worse as the condition becomes more chronic.

Taking a wait-and-see approach is not uncommon when horsemen see swelling in the back legs, thinking their horses are just a bit off and need a few days' stall rest. Spier warns that this is the wrong approach.

"The infectious form of lymphangitis can affect all horses, including Thoroughbreds, and is something that a lot of horse owners are not familiar with, but it's definitely out there," she said. "If that leg is swollen, is painful to the touch, or the horse is lame, then it should be considered a medical emergency, and the vet should be called."

Bacteria, foreign substances, or inorganic material introduced as a result of an injury such as a kick are usually the cause of the infectious form of lymphangitis.

"However, there are often times when we don't know the cause because we are just presented with a horse with a big leg and there is nothing draining," Spier said. "In that case, there is no way to culture it, so a vet would just prescribe broad-spectrum antibiotics."

In the early stages of lymphangitis, diagnosis usually is made by physical examination. "If the horse has an edema in the legs, usually it is painful on palpation [manual examination]," she said. "Most times, there is an associated wound, puncture wound, or a scrape where bacteria have gained entry through the skin. You can also feel what we call a 'corded' lymphatic, where the swollen lymphatics take on a ropey or corded feeling."

First response

Should your horse have an injury on the lower leg, Spier said the first step is to locate the wound and clean it. Then apply a good antiseptic wound dressing and wrap it.

"If there's a puncture present, that's when you want to call a vet, because there are so many structures on the hind leg and joint capsules, you wouldn't want to delay having veterinary treatment for a puncture wound," she said.

In cases of late or inadequate treatment, the development of scar tissue throughout the tissues and the lymphatic system limits the leg's ability to return to normal size, resulting in a thickened and scarred leg, even after the infection is brought under control.

Spier said that, if lymphangitis is suspected, treatment would consist of local wound therapy and systemic antibiotics for seven days to several months, depending on what the veterinarian believes is the most likely cause.

"However, horses diagnosed with ulcerative lymphangitis should be treated early and aggressively with antimicrobials, or else residual lameness or limb swelling may occur," Spier said.

Ulcerative lymphangitis

A more severe form of lymphangitis is caused by Corynebacterium pseudotuberculosis, which attacks the horse's lymph system and causes painful swelling accompanied by abscesses that break out in several places over the swollen leg. Brought about by the invasion of harmful bacteria, typically in the fetlock region of the hind limbs, this condition is referred to as ulcerative lymphangitis, which derives its name from the appearance of oozing ulcers that erupt on the leg.

"Ulcerative lymphangitis, or limb infection, appears as a severe cellulitis, affecting one or more limbs accompanied by multiple draining, ulcerative lesions," Spier said. "Cellulitis, which is an infection in the tissues, is often a precursor to lymphangitis. Horses with ulcerative lymphangitis often develop a severe lameness, fever, lethargy, and anorexia. There appears to be no breed or sex preference for the development of this infection."

Accompanied by lameness, heat, pain, and the telltale swelling ulcers that often break and drain, this soil-borne bacterial organism invades the lymphatic system through abrasions or wounds in the skin or mucous membranes. This disease can be spread through the introduction of infected horses into a herd and can be prevented by cleaning and disinfecting limb injuries, as well as good hygiene in stables.

Horses with ulcerative lymphangitis should be treated early and aggressively with medical therapy involving antimicrobials and anti-inflammatories to combat the infection. Physical therapy, including hydrotherapy, hand walking, and wraps, as well as the administration of nonsteroidal anti-inflammatory drugs such as phenylbutazone (Bute) or flunixin meglumine (Banamine), also are recommended.

Lymphangitis can be a frustrating problem brought on by a large number of potential causes affecting the lymph system. While treatment can be difficult and is usually long term, early recognition of the infection is the key.

"The most important thing is early recognition in order to rule out the presence of infection," Spier said. "Certainly, there are a lot of horses that just stock up or have been worked harder than the degree that they're trained. They can have some limb swelling, and it should be nothing to be alarmed about. But if there's any associated lameness or the edema itself is painful on palpation, then you definitely want to seek out a vet."