Swelling in the lower legs of horses is a common event and can be a bit of a diagnostic and therapeutic dilemma do to the many different causes. This article discusses the diagnosis, causes, and treatment of the various causes of this condition. These include: lymphangitis, cellulitis, snake bite, photosensitization, purpura hemorragica, and Equine Viral Arteritis (EVA). If you are having trouble with swellings that are cool and not associated with fever and/or pain see: The Diagnosis of Swellings in Horses.

When presented with a horse that has a hot, swollen, and painful leg(s) there are at least these possibilities:

• Dermatitis: inflammation of the skin
• Cellulitis: inflammation of the connective tissue just under the skin.
• Damage to the deeper supporting strucutres of tendons, ligaments, and/or bones.
• Foot abscess causing swelling that goes up the leg.

These are very different conditions that can look remarkably similar. Some dermatological conditions can cause remarkable reaction and secondary swelling of the leg. A damaged flexor tendon can cause remarkable heat and swelling at the skin. Cellulitis simply means inflammation of the tissues and there are many possible causes of cellulitis in one or more of the legs of horses. Cellulitis in the legs is characterized by swelling, heat, and pain in the affected legs. Often fever is present. There will be lameness, possibly to the point of non-weight bearing. With severe distension of the skin of the legs, serum can weep through the skin, necrosis of the skin and , and the skin splitting open can occur. Founder can occur secondary to the inflamed leg or in the opposite leg due to bearing more weight than the laminae can tolerate.

Therefore a complete history and physical exam is needed to differentiate the causes for this condition. Included in the history is recent exposure to vaccines particularly Strangles or Strangles vaccination, recent shoeing, which came first the lameness or the swelling, recent accidents, and whether or not there is a possible exposure to Equine Viral Arteritis (EVA). The physical exam should include a thorough examination of the sole for abscesses, the leg for puncture wounds, the skin for signs of superficial skin diseases, and the sclera and mucous membranes for signs of systemic vasculitis.

An important differentiating characteristic is whether the problem is one, two or more legs. When one leg is affected it suggests a local problem, like infection or trauma. When two of more legs are affected it suggests this may be a systemic disease like immune disorders (secondary to vaccination for instance) or viral infections (Influenza, EVA, etc). As a result once it is determined inflammation is the cause of the swelling and foot abscess ruled out consider the following diagnostic possibilities based on whether one or more legs is affected.