Equine Disease Quarterly | EQUINE
Guttural Pouch Mycosis
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 (Figure 1). Guttural pouch
mycosis (GPM) is a potentially life-threatening disease
that may initially present as a simple nosebleed
(epistaxis) 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, unilateral
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, resulting in hemorrhage
from the internal carotid, occipital, or maxillary arteries.
Severe hemorrhage may result in rapid death from
exsanguination. Dysphagia as well as various forms of
pharyngeal dysfunction in GPM result from mucosal
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 horses.
Wet environmental conditions, prolonged treatment
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
predilection has been reported, the disease is more
common in mature horses, but has been documented
in foals as young as two months of age.
Figure 1. Fungal infection of guttural pouch. (Image courtesy
of Dr. Nathan Slovis)
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 hypoglossal.
Neurological dysfunction of the pharynx results when
the nerves within the guttural pouch are inflamed or
fibrosed. Generally, the presence of dysphagia or other
neurological deficits at presentation indicates a poor
prognosis. The severity of cranial nerve deficits depends
on whether nerve injury is restricted to a local neuritis
or necrosis of the nerve secondary to fungal infiltration
and fibrosis.
Treatments include both medical and surgical
options. While there are reports of successful medical
treatment of GPM with systemic and topical antifungal
medications, medical treatment is generally considered
to be less efficacious than surgical treatment.
• Volume 21 Issue 4 | December 2019 •
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