There are three forms of lymphangitis: sporadic, ulcerative and epizootic.
Sporadic is the most common in the UK.
Ulcerative is, thankfully, more rare and as the name suggests leads to abscesses under the skin which can burst out as ulcers.
Epizootic is a notifiable disease in the UK (last reported in 1907) and is caused by a fungal infection.
Sporadic lymphangitis in horses can extremely problematic. It is inflammation of the lymph vessels most usually in the limbs and in the majority of cases, the hindlimbs. The lymphatic system includes lymph nodes and lymph vessels (similar to veins) containing “lymph” which is basically the fluid part of blood (without the red blood cells). Its main function is to remove extra fluid from the lower limbs and help to prevent infection.
There appears to be a problem with the horse’s immune system that allows the condition to occur. Generally, however, there is a break in the skin, evident as a wound (sometimes not a recent one and often innocuous in appearance), dermatitis such as mudrash or even cracked heels; this allows infection to get through the epidermis and into the lymphatic system. Once the infection gains access to the lymph vessels, it can spread up the leg causing widespread inflammation that not only restricts drainage causing the leg to swell, but also causes a great deal of pain. Initially, the lymph vessels can appear as painful thick cords but as the disease progresses the swelling increases and there is a loss of definition of the joints and it can, in severe cases, appear like a “tree-trunk” leg. As the leg swells there is usually intense pain leading to severe lameness and they often become non weight-bearing on the leg. Frequently fluid (serum) leaks from the leg due to the pressure and this may dry as scabs on the skin.
In long term or recurrent cases there is scarring and breakdown of the one-way valves within the lymph vessels (almost like varicose veins in humans) leading to permanent swelling of the legs. Once this happens the condition never resolves and movement is restricted. A high temperature or fever is a common finding with lymphangitis and often the horse appears clinically ill; they are depressed, may reduce their food intake or not eat at all.
Early intervention and prompt treatment is essential to prevent irreparable damage.
A swab may be taken from the wound or skin (especially if serum is weeping) for bacterial culture and sensitivity; this allows the targeted use of antibiotics against sensitive bacteria. The choice of antibiotic is important because of the increase in bacterial resistance; systemic, injectable antibiotics are often used for a quicker effect and to ensure the full dose is received and there is no reliance on a sick horse eating oral antibiotics.
A technique called intravenous regional therapy (IVRT) may be used to concentrate the antibiotic in the affected limb in conjunction with the systemic antibiotics. IVRT involves the use of a tourniquet and commonly the antibiotic of choice is gentamicin given using a cannula into the vein; it may be difficult to use this if the veins are occluded.
It is vital to give antibiotics immediately as well as a non-steroidal anti-inflammatory drug (NSAID) such as flunixin or phenylbutazone (“bute”); in severe cases steroids may be used initially although there are concerns that longer term steroid use will reduce the ability to fight the infection or cause laminitis. Despite these concerns and because of the potential consequences of lymphangitis, steroids are frequently used with a great deal of success. They are more potent anti-inflammatory drugs than NSAID’s and often substantially improve the leg and, very importantly, reduce the tremendous pain commonly felt in these cases.
Topical skin treatment of the wounds, dermatitis or scabs (using antibacterial or antiseptic washes and creams) is important to prevent ongoing infection and bandaging (with thick padding beneath) is important to help reduce the swelling. It is vital to use a large amount of thick padding such as cotton wool or cotton wadding under the bandage.
Exercise is very important to help improve the circulation thereby reducing swelling; although the initial few steps can be very painful there is usually a rapid improvement.
Other treatments may include diuretics such as frusemide to reduce the fluid, potassium iodide solution (orally for dermatitis) or intravenous DMSO.
Prevention can be more difficult, particularly once lymphangitis has occurred and caused some permanent scarring. Obviously hygiene and cleanliness of the skin has got to be scrupulous; any wounds must be addressed immediately.