It can be a startling discovery to find your horse with one leg doubled in size and non-weight-bearing. Don’t panic. Call your veterinarian, and be prepared with answers to questions he or she might ask:
- Where is the swelling located?
- Does it include any joints?
- Is it the same on both sides of the leg?
- Any wounds?
- History of trauma?
- Was your horse wearing bandages or boots?
- How lame is the horse?
- Any recent injections?
- Have you applied a topical ointment or salve to the leg?
- Does your horse have a fever?
- Is the area warm or hot, firm or soft?
- Does light or firm pressure cause pain?
- Is there any drainage or leaking?
- Has this happened before?
Cold hose the limb, and prevent your horse from moving around, if possible, until your vet arrives.
The most common causes of acute severe lameness include abscesses, fractures, laminitis, septic (infected) joints, or cellulitis. The latter is an infection within the subcutaneous skin layer (contains connective and fat tissue), not regular edema (fluid swelling). Certain clues can indicate your horse has cellulitis. First off, the limb will be very painful to the touch—to the point your horse might pull his leg away so quickly he hops sideways. It will be firm and hot. He’ll be very lame, though most of the pain occurs when he moves the limb, due to the pressure. In some mild cases the horse might be able to bear weight on it. Most affected horses have a fever. In comparison, a horse that is “stocked up” is not severely lame and typically has a softer, cooler swelling called pitting edema (pressing it leaves an indent).
Cellulitis can be rapidly progressive if you don’t address it quickly. It often affects only one limb, most frequently a hind limb. Severe cases can cause abscessation, resulting in ulceration, skin sloughing, and even bone and synovial (joint) tissue infection. Cellulitis can progress to inflammation of the lymph vessels, known as lymphangitis, which can permanently damage the lymphatic circulation and make cellulitis more likely to occur in the future. Other complications can include thrombosis of the small vessels resulting in tissue necrosis (death), supporting-limb laminitis, and sepsis.
So, what causes this subcutaneous disruption? The inflammation had to start somewhere. Most cases involve bacteria entering through undetectable microtraumas to the skin, though cellulitis can also occur following an injection. A Staph infection can occur from blunt trauma alone. Pastern dermatitis (aka scratches) is a common culprit. Veterinarians have also noted cases following application of a poultice or topical counterirritant that resulted in cellulitis and skin necrosis 48-72 hours later.
Treatment involves reducing inflammation, controlling the infection, and preventing further infection. Your veterinarian might ultrasound the leg to look for foreign bodies or fluid pockets. He or she might open the skin or wound to allow for drainage—critical for any wound, necrotic/infected area, or abscess—and debride (remove damaged tissue) and lavage (flush) the area as necessary. Your horse should receive non-steroidal anti-inflammatories such as phenylbutazone or flunixin meglumine. In the case of a noticeable wound, fluid pocket, or drainage, your veterinarian might also collect a culture or use a Gram stain to choose the appropriate antibiotic, though this is not always possible.
In very severe cases veterinarians might administer steroids or diuretics. Pentoxifylline can increase blood flow. If you still detect heat and pain in the limb, perform hydrotherapy. Though often not possible in the acute phase, moving around is beneficial for the horse; the stretch and release of the muscle tendon unit helps stimulate lymphatic resorption and outflow. Depending on the rate and severity of progression, you might apply a bandage or a sweat if your horse will tolerate it. Monitor the bandage to ensure it does not become restrictive. Persistent cellulitis of more than a week might result in a chronic enlarged limb.
Ways to prevent recurrent cellulitis include monitoring for and cleaning wounds properly. If lymphatic damage has occurred, any future wound can potentially cause cellulitis. Other preventative measures include keeping the skin dry. You might place gravel in paddock areas that tend to get muddy to reduce moisture. Avoid drying out skin, however, with shampoos that might lead to cracking. Finally, keep the horse moving regularly and exercise him to maintain circulation.