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
[phone]
Veterinary Diagnostic Laboratory
University of Kentucky
Lexington, Kentucky