Equine lymphangitis

Equine lymphangitis is an inflammation or swelling associated with impairment of the lymphatic system, particularly in a limb, in horses. It is most commonly a bacterial infection, although bacterial culture may be negative.

Often referred to as fat/big leg disease, it is sometimes known as weed or Monday morning disease (not to be confused with the more common usage of MMD referring to exertional rhabdomyolysis or azoturia). This article refers mainly to sporadic lymphangitis. Ulcerative lymphangitis is referred to in passing, as it is managed in a similar manner. Epizootic lymphangitis is similar to glanders, but caused by the fungus Histoplasma farciminosum.

Corynebacterium pseudotuberculosis has been cultured from some cases (particularly of ulcerative lymphangitis; however, in others, bacterial culture is negative. This may be because:

Of these, a) is thought to be the most likely, and d) the most improbable.

Extreme swelling of a limb, usually a hind limb, is seen, often as far proximally as the hock, or occasionally as far proximally as the stifle. In some cases, swelling continues through the udder or sheath and along the subcutaneous abdominal veins. In the early stages, the swelling is primarily a "pitting oedema"; in other words, if pressed, a depression remains in the skin of the limb. The affected leg may reach twice or even three times its normal size, and may be very sensitive to the touch. In chronic cases, much of the swelling is firm, as scarring and fibrosis occur.

Lymphangitis is commonly associated with a wound, which may be very minor. This is a likely entrance for bacterial access to the lymph ducts. The degree of lameness is variable, but may be sufficient to give the impression of a fracture. The horse may or may not be pyrexic (fevered). The limb may occasionally ooze serum.

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