CELLULITIS OR LYMPHANGITIS?
Cellulitis and lymphangitis may seem very similar—both cause dramatic and severe swelling that tends to affect the lower hind leg—but they are distinctly different conditions. Cellulitis is an infection of the connective tissues under the skin, while lymphangitis is an inflammation of the lymphatic vessels.
“Chronic lymphangitis usually refers to a sterile edema [fluid accumulation], with no infection,” says Margaret Mudge, VMD, of Ohio State University. Cellulitis, on the other hand, is an infection. “Probably the more proper term would be ‘septic cellulitis,’ meaning a bacterial infection under the skin, versus a lymphangitis,” she adds. “It can become a bit confusing and complicated, however, because there are types of lymphangitis that are associated with infectious agents. But usually when we are using this term we refer to just the edema and lack of lymphatic return, versus cellulitis [infection].”
The signs of lymphangitis are also subtly different from cellulitis.
• Although the condition causes dramatic swelling, a leg affected by lymphangitis is typically not hot from an infection, nor is it as painful. A horse with lymphangitis may move stiffly, but he is not likely to be truly lame.
• The swelling takes longer to develop. “With cellulitis you suddenly find the horse with a huge leg, but with lymphangitis, it’s more insidious and slowly progressive,” says Callie Fogle, DVM, of North Carolina State University. “The legs may have some scabs or scratches [pastern dermatitis] on the back of the fetlocks and pasterns. Those crusts and scabby areas may be a sign that lymphatic drainage is not effective. Like a horse with chronic cellulitis, a horse with lymphangitis is also unable to fight infection or mount a good response against invading bacteria in the distal limbs.”
• Lymphangitis is also likely to affect more than one leg. “Lymphangitis is more likely to be bilateral, affecting both front legs or both hind legs or even all four limbs,” says Fogle. “Usually the hind limbs are worse, but we do occasionally see cases in which the forelimbs are worse.”