Walking On Volume 6, Issue 2, February 2019 - Page 6

For the Health of It Cutaneous Lymphangitis Reprinted with permission from the April 2018 issue of Equine Disease Quarterly The lymphatic system is an important component of the car- diovascular system and consists of lymphatic vessels, lymph nodes, tonsils, spleen, and thymus. Lymph, which is a clear colorless fluid, is formed from fluid loss that occurs during normal nutrient exchange in capillary beds. Lymph is transport- ed by lymphatic vessels to regional lymph nodes for filtration to aid in immunologic detection of micro- organisms, toxins, and foreign material. Once filtered, the lymph is again transported by lymphatic ves- sels to large veins, which ultimately return it back into the circulatory system to replenish the fluid lost from the capillaries. Lymphatic dis- ease can occur when lymph vessels become inflamed, leaky, and/or blocked. Cutaneous lymphangitis—in- flammation of lymphatic vessels of the skin—is fairly uncommon in horses, does not exhibit age, sex, or breed predilections, and can develop from both infectious and non-infectious causes. Clinically, cutaneous lymphangitis can man- ifest as a swollen limb, skin abnor- malities characterized as multiple skin nodules that can abscess or develop draining tracts, and/or lameness. Cutaneous lymphangitis typically affects the distal portion of a single hind limb, between the hock and hoof. Due to the char- acteristic appearance of affected limbs, the disease is commonly referred to as “big leg” or “fat leg.” Infectious cutaneous lymphan- 6 • Walking On gitis has traditionally been associ- ated with poor hygiene and insect transmission of microorganisms. It is sporadically diagnosed in horses, but sometimes occurs simultane- ously in multiple horses on the same farm. Infection of the lym- phatic system develops following contamination of skin wounds by various bacteria, most commonly Corynebacterium pseudotubercu- losis (the causative agent of ulcer- ative lymphangitis/pigeon fever). However, pure or mixed infections with other bacteria, such as Staph- ylococcus sp., Streptococcus sp., Trueperella pyogenes, Rhodococ- cus equi, Pasteurella haemolytica, Pseudomonas aeruginosa, Fuso- bacterium necrophorum, Actino- bacillus equuli, and Burkholderia mallei (the cause of glanders) can also result in cutaneous lymphangi- tis. Additionally, pathogenic fungi such as Sporothrix sp. (the cause of sporothricosis) or Histoplasma farciminosum (the cause of epizo- otic lymphangitis) also have been associated with lymphatic system infection. The USA is currently free from glanders and epizootic lymphangitis. Treatment of in- fectious cutaneous lymphangitis includes appropriate antimicrobials, non-steroidal anti-inflammatory drugs, hydrotherapy, and surgical fluid drainage. Cutaneous lymphangitis can become chronic if left untreated or if treatment is ineffective. Chronic expansion of the subcutis by edem- atous fluid due to faulty lymphatic vessels can result in the deposition of fibrous tissue and permanent limb disfigurement. This emphasiz- es the importance of rapid diag- nosis and treatment of cutaneous lymphangitis. Sporadic lymphangitis, also known as “Monday morning leg,” can also result in swollen distal hindlimbs. This condition can develop in horses that are stabled or immobile for extended lengths of time, typically days or more. The cause of sporadic lymphangitis is not well understood, but luckily the condition typically resolves after exercise. Cutaneous lymphangitis is occa- sionally diag- nosed at the Univer- sity of Kentucky Veterinary Diag- nostic Laboratory. However, the exact frequency of the condition cannot be easily estimated through typical diagnostic submissions, because diagnoses are frequently made by veterinarians in the field and don’t require extensive diag- nostic evaluations. CONTACT: Dr Alan Loynachan alan_loynachan@uky edu (859) 257-8283 Veterinary Diagnostic Laboratory University of Kentucky Lexington, Kentucky