Page 722 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Respir atory system: 3.4 Medical conditions of the lower respir atory tr act 697

VetBooks.ir OBSTRUCTIVE CONDITIONS

Recently, the term equine asthma syndrome has been
ratory diseases (upper airway obstruction, viral
used to incorporate two inflammatory conditions of dysfunction, neurological disorders and other respi-
the airways of adult horses, with distinct phenotypes. infection, bronchopneumonia, exercise-induced pul-
Inflammatory airway disease (IAD) refers to the monary haemorrhage, lungworm, neoplasia), should
milder form that occurs in younger horses, whereas be considered.
the more severe form is called heaves, or recurrent
airway obstruction (RAO). Both conditions are dis- Diagnosis
cussed in the sections below. Careful auscultation of the thorax during use of
a re-breathing bag may reveal the presence of
INFLAMMATORY AIRWAY DISEASE increased bronchial tones, wheezes and/or crackles,
as well as movement of secretions during tracheal
Definition/overview auscultation. Absence of these signs does not, how-
IAD (otherwise known as non-septic IAD) is an ever, preclude a diagnosis of IAD. Often, no abnor-
inflammatory process of the lower airways that malities are detected with even a thorough physical
causes pulmonary dysfunction and reduced exercise examination.
tolerance in affected horses. Radiography is of no diagnostic use to confirm
IAD, although radiographs may help to exclude
Aetiology/pathophysiology diagnoses of bronchopneumonia or pulmonary
Multiple inciting agents have been proposed as causes abscessation. Bronchoscopy is useful to assess airway
for the small-airway inflammation in young horses hyperreactivity, hyperaemia, oedema and broncho-
with IAD, including recent viral infection, exposure constriction, and to evaluate the presence and nature
to environmental irritants (e.g. dusts, noxious gases) of any airway secretions (Fig. 3.155).
or sources of endotoxin and pulmonary haemor-
rhage. Some clinicians have speculated on the role
of bacteria, particularly in racehorses. An association 3.155
has been reported between the presence of bacteria
in tracheal aspirate samples and IAD; however, a
causal relationship has not been proven and there is
insufficient evidence to confirm an infectious cause
of this condition. Currently, the exact pathophysiol-
ogy of this condition remains unknown. It is most
likely multifactorial in nature.

Clinical presentation
Reduced athletic performance and/or prolonged
time for recovery from exercise are frequently the
only presenting signs. Nasal discharge may be pres-
ent, ranging from serous to mucopurulent, and
coughing may be observed during exercise or at the
time of feeding. Clinical signs of respiratory diffi-
culty are absent at rest in horses with IAD.
Fig. 3.155 Bronchoscopic view of the carina in
Differential diagnoses a horse with IAD. Mucus is visible at the tracheal
Other common causes of reduced performance, puddle (red arrow), and the carina is blunted due to
particularly musculoskeletal abnormalities, cardiac oedema (white arrow).