Equine lymphangitis

Equine lymphangitis is an inflammation or swelling associated with impairment of the

may be negative.

Often referred to as fat- or 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

). 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.^[1]

Causes

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

• a) The micro-organism responsible is difficult to culture (e.g. many Mycoplasma species).
• b) The organism has been effectively eliminated by the immune system and the pathology is due to an excessive immune response after the organism has been cleared.
• c) The organism is not a bacterium, but a fungus, so is very difficult to culture.
• d) The disease has another cause.

Of these, the first is thought to be the most likely, and the last is least likely.

Clinical signs

Extreme swelling of a limb, usually a hind limb, is seen, often as far proximally as the

"; 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

(fevered). The limb may occasionally ooze serum.

In ulcerative lumphangitis, "cording" of the lymphatics and the formation of hard nodules and abscesses may also occur; occasionally, a greenish, malodorous discharge is present. In the US in particular, the disease may be characterised by multiple small, open sores.^[2]

Diagnostics

is worth trying, but is often unrewarding.

Treatment

The mainstays of treatment are the administration of

In ulcerative lymphangitis,

Physical therapy is also important, particularly maintaining movement by walking out and massage to improve lymphatic drainage and reduce the oedema. Bandages may also be useful, as may cold hosing in the initial phase. A sweat bandage or poultice is often applied. An overly tight bandage should not be applied, as swelling may continue, decreasing circulation through the limb, and potentially causing a bandage-bow. After-care often is advised to include consistent turnout and exercise.

Outcome

The initial pain and lameness usually respond rapidly to treatment, but the swelling may persist for many weeks. In addition, once a horse has had an episode, it appears to be predisposed to recurrence, and may suffer from "filled legs" permanently – i.e. if left in a stable and relatively immobile, poor lymphatic circulation results in a passive oedema of the previously affected limb, that dissipates on exercise. In more severe cases, the limb may never return to normal size. In these cases, permanent scarring of the lymphatics and other tissues is likely. Treatment in these cases is unrewarding, and euthanasia may be indicated if the condition causes unmanageable lameness.

References