Page 723 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

698 CHAPTER 3

VetBooks.ir 3.156 3.157

Fig. 3.156 Cytology of BAL fluid from a normal Fig. 3.157 Cytology of BAL fluid from a horse with
horse. Pulmonary alveolar macrophages are the IAD. Leucocytes are seen trapped in mucus. Mast cells
predominant cell type (arrows). (black arrows), an eosinophil (red arrow) and granules
from globular leucocytes (white arrows) are present.
3.158
correlate poorly between samples obtained via tra-
cheal aspirate versus BAL.
Pulmonary function testing (open plethysmog-
raphy with histamine bronchoprovocation) can be
beneficial for confirming the diagnosis in horses
with suspected IAD and equivocal BAL results.

Management
The key to recovery from IAD is adequate rest of
affected horses and environmental modification
to significantly reduce exposure to respirable par-
ticles (Table 3.3). Many recommendations regard-
Fig. 3.158 Cytology of BAL fluid from a horse ing medical therapy for IAD are extrapolated
with IAD. Multiple eosinophils are present (black from studies in heaves-affected horses. Treatment
arrows). Pulmonary alveolar macrophages containing includes inhalation therapy with mast-cell stabi-
eosinophilic granules in phagosomes are also visible lisers (Fig. 3.159) and/or corticosteroids depend-
(red arrows). ing on the type(s) of cell identified on the BAL
differential count. Oral and parenteral corticoste-
BAL is the test of choice to diagnose IAD. roids may instead be used to reduce cost, but they
Cytological assessment of BAL fluid is required to require a higher overall dose to be administered
determine the type(s) of leucocyte contributing to to the animal and present the possibility of side-
the airway inflammation. In general, IAD is charac- effects. Bronchodilators may also be useful prior
terised by elevations in the percentage of eosinophils, to light exercise but should be avoided during peri-
mast cells and/or neutrophils in the differential cell ods when the animal is housed indoors (Table 3.4).
count (Figs. 3.156–3.158). Cytological assessment Low-dose interferon-alpha has been shown to
of fluid obtained by tracheal aspiration is not an ade- improve the outcome in horses with IAD in two
quate substitution for BAL, since cell populations recent studies.