Some type of trauma can lead to a frustrating equine disease called lymphangitis

FEW OTHER conditions in the horse look like lymphangitis and, once you have seen a case of it, you probably will not forget its more common name: stovepipe leg.

Horses affected with lymphangitis have a swollen leg that loses all distinction and resembles a stovepipe. If this clinical appearance is not remarkable enough, lymphangitis is even more unforgettable because--though it has been recorded for centuries and is easy to diagnose--its cause is still largely unknown.

Most cases of lymphangitis start with some type of trauma. Horses with deep cuts or puncture wounds can develop the condition; bites from spiders, scorpions, and any type of insect or animal can initiate it. Introduction of foreign objects, such as slivers of wood, plant material (thorns or prickers), glass, or other similar objects, also are believed to contribute to some cases of lymphangitis. The actual cause of specific cases of lymphangitis is often difficult to determine because affected horses are usually noticed after massive swelling has occurred, and finding a small bite or puncture usually is impossible.

Hot, tender, swollen leg

In a typical scenario in cases of lymphangitis, a previously healthy horse is put in its stall at night or turned out with no problems noted. In the morning, the horse has one massively swollen leg, usually a hind one, which is hot and tender. Attempting to touch the leg may cause the horse to flex the leg and resist contact. This response can be so severe the horse might come close to falling over toward the unaffected side.

In early stages, these horses might have an elevated temperature (in the 103-degree range) and might be off their feed or even slightly colicky due to pain. Close examination of the affected leg will show swelling and tenderness along the main blood vessels on the inside of the leg. The fact that swelling and tenderness follow the anatomical location of the large veins and arteries of the leg has led veterinarians to postulate some blood-borne agent or toxins as the initial cause of the condition.

Affected horses will have difficulty moving and might only place the toe of their affected leg on the ground. Massive swelling soon develops and might stretch from the coronary band to the upper thigh. There is usually a sharp line of demarcation to the upper swelling, and a shelf-like division between the normal leg and the swollen leg exists at that point.

As swelling becomes more pronounced over the first 48 hours, the skin of affected legs may crack or split over pressure-point areas. Any areas where the leg usually bends are at risk, and cracks are frequently seen at the front coronet, the front of the hock joint, and even over the front of the fetlock on occasion. Cracks will ooze a honey-colored to creamy white sticky serum.

Banamine first choice

In typical cases, these swollen legs will gradually resolve. Cracked skin will heal and the horse will begin to use the leg normally. Treatment consists of both medical and supportive care. A veterinarian initially will treat a case with pain relievers and anti-inflammatory drugs. Bananime (flunixin) is the first drug of choice because of its anti-inflammatory and antiprostaglandin effects.

Phenylbutazone will be used secondarily to control pain and reduce swelling. Because open, cracked skin is an invitation to bacterial infections--and because the true cause of lymphangitis is still unknown--antibiotics are often used, as well.

Intravenous oxytetracycline produces excellent serum antibiotic levels and is commonly used in cases. Intravenous dimethylsulfoxide (DMSO) is used by many clinicians because of its ability to reduce swelling and to help control tissue damage on a cellular level.

Simple supportive measures also are important. Frequent hosing of the affected leg is necessary. Applying a moisturizing cream to swollen, cracked skin is important. Massaging the area can be helpful and hand walking and gentle exercise, as tolerated, eventually will help the horse to regain normal range of motion.

Uncomplicated cases of massive swelling due to lymphangitis can be impressive and might take some time to resolve, but they usually respond well and the horse returns to full function.

"The really frustrating cases are horses with recurrent lymphangitis," said Michelle Barton, D.V.M., Ph.D., a board-certified internal medicine specialist at the University of Georgia.

These horses may improve and become sound, but their thick leg remains. Adding to the frustration is the fact the horses will have repeated bouts of lymphangitis in the affected leg. Periodically, with no discernable pattern of inciting cause, they will develop a hot and massively swollen leg again and will go through the entire lymphangitis sequence.

Veterinarians have been searching for an infectious agent or some physical agent in the leg that causes these repeated flare-ups, but to no avail. Barton even has examined these horses postmortem.

"I have done detailed dissection of the legs of some of these horses following their deaths in an attempt to find a foreign body or site of infectious material," Barton said, "but I have never been able to find the source for these recurrences."

Possible neurotoxins, as seen with snake and insect bites, can affect blood flow through tissues, and these agents have long been thought to be involved in recurrences, but no proof has been found. Viral recurrence, such as is seen with herpesvirus and the skin condition in humans known as shingles, also has been considered, along with a slow, smoldering infection. Intense efforts to isolate both bacteria and viruses from the tissue of these horses has been unrewarding.

Additional options

Despite being unable to diagnose the exact cause of lymphangitis, Barton provides some additional treatment options based on recent case research. She has been using Trental (pentoxyphylline) to help peripheral blood flow in affected horses. This drug, also used in cases of laminitis, helps improve blood flow in damaged vessels by making red blood cells better able to move through narrowed areas. Improved blood flow helps reduce swelling and improves the overall appearance and function of the leg.

Barton also uses Naquazone (a combination of Salix and dexamethazone) to help reduce the massive swelling in lymphangitis cases. Salix, a diuretic, causes the body to excrete fluid through the urine. Fluid in the swollen leg is pulled out of tissues and removed under its influence. Dexamethazone, a steroid, helps reduce inflammation and improve blood flow. While not curative, these two drugs seem to improve the horse's response in difficult cases, Barton said.

Because the cause of lymphangitis is unknown, prevention is difficult. Good management to reduce contact with snakes, insects, and other sources of trauma will help. Quick recognition and treatment for suspected cases might help reduce the eventual swelling. Aggressive treatment with vasoactive agents could reduce the number of recurrent cases, and hopefully future research will uncover a specific cause to this often spectacular, but frustrating disease of horses.