Walking On Volume 6, Issue 10, October 2019 | Page 8
For the Health of It
Guttural Pouch Mycosis
Reprinted with permission from Equine Disease Quarterly, Volume 28, Number 4
Airway dysfunction is one of many causes of poor
performance in equine athletes. Airway dysfunction
can be classified as either acquired or developmental.
One acquired dysfunction that is generally overlooked
is a fungal infection of the guttural pouch, known
as guttural pouch mycosis. Guttural pouch mycosis
(GPM) is a potentially life-threatening disease that
may initially present as a simple nosebleed (epistax-
is) or even poor performance in an equine athlete.
GPM has been documented in various parts of the
United States, particularly in the southeast, as well as
the United Kingdom. Clinical signs include unilateral
(one-sided) or bilateral (both-sided) epistaxis, unilat-
eral nasal discharge, dorsal displacement of the soft
palate, dysphagia (difficulty swallowing), and laryngeal
hemiplegia (partial or total paralysis of the larynx).
Epistaxis occurs due to erosion of the guttural pouch
mucosa by a fungal plaque, result- ing in hemorrhage
from the internal carotid, occipital, or maxillary arter-
ies. Severe hemorrhage may result in rapid death from
exsanguination. Dysphagia as well as various forms of
pharyngeal dysfunction in GPM result from muco-
sal penetration and damage by fungal hyphae to the
glossopharyngeal, hypoglossal, and/or the pharyngeal
branches of the vagus nerves. A variety of fungi have
been isolated from GPM with Aspergillus spp. being
common. Aspergillus spp. and other opportunistic
fungi are found naturally in the environment and can
be found in the upper respiratory tract of normal hors-
es. Wet environmental conditions, prolonged treat-
ment with antimicrobials, an immunocompromised
host, or use of corticosteroids have been proposed as
factors conducive for fungal overgrowth. It is not fully
understood why mycosis occurs in animals that are not
immunosuppressed or debilitated. While no age predi-
lection has been reported, the disease is more common
in mature horses, but has been documented in foals as
young as two months of age.
Dysphagia is the second most common clinical
sign associated with GPM, after epistaxis. The cranial
nerves within the guttural pouch that innervate the
pharynx are the glossopharyngeal, vagus, and hy-
poglossal. Neurological dysfunction of the pharynx
8 • Walking On
results when the nerves within the guttural pouch are
inflamed or fibrosed. Generally, the presence of dys-
phagia or other neurological deficits at presentation in-
dicates a poor prognosis. The severity of cranial nerve
deficits depends on whether nerve injury is restricted
to a local neu-ritis or necrosis of the nerve secondary
to fungal infiltration and fibrosis.
Treatments include both medical and surgi- cal op-
tions. While there are reports of successful
medical treatment of GPM with systemic and
topical antifungal medications, medical treat- ment is
generally considered to be less efficacious than surgi-
cal treatment. Topical treatments with enilconazole
and miconazole have been used with success in some
cases. The presence of a diptheritic membrane (necrot-
ic material over the surface of the fungal plaque) may
prevent penetration of systemic antifungals. Addition-
ally, there is increased risk of fatal hemorrhage due to
the longer course of medical treatment. The preferred
method to treat severe guttural pouch mycosis is to
surgically insert a coil or balloon into the affected
blood vessel to quickly cut off the blood supply. Typ-
ically, once the blood supply has been removed, the
fungus regresses.
CONTACT:
Nathan Slovis, DVM, Dipl . ACVIM,
CHT (Certified Hyperbaric Technologist)
(859) 253-0002
Hagyard Equine Medical Institute Director
McGee Critical Care and Medical Center
Lexington, KY