Page 361 - Small Animal Internal Medicine, 6th Edition

CHAPTER 21 Disorders of the Trachea and Bronchi 333

mounting that in people these drugs have antiinflammatory TRACHEOBRONCHOMALACIA
properties. (COLLAPSING TRACHEA)
VetBooks.ir ans in the use of oral leukotriene inhibitors in cats (e.g., Etiology
Much interest has been shown by clients and veterinari-
Accolate, Singulair, Zyflo). However, the clinician should be
(see Figs. 21.7, B, and 20.27, A). An open lumen is main-
aware that in people, leukotriene inhibitors are less effective The normal trachea is seen to be circular on cross section
than glucocorticoids in the management of asthma. Their tained during all phases of quiet respiration by the cartilagi-
main advantages for people lie in decreased side effects, com- nous tracheal rings, which are connected by fibroelastic
pared with glucocorticoids, and ease of administration. To annular ligaments to maintain flexibility, thereby allowing
date, toxicity studies have not been performed on these movement of the neck without compromising the airway.
drugs in cats. Furthermore, several preliminary studies The cartilaginous rings are incomplete dorsally. The dorsal
suggest that leukotriene inhibition in cats would not be tracheal membrane, consisting of the longitudinal tracheal
expected to have efficacy comparable with that in people. muscle and connective tissue, completes the rings. The term
Therefore routine use of leukotriene inhibitors in cats is not tracheal collapse refers to narrowing of the tracheal lumen
currently advocated. resulting from weakening of the cartilaginous rings, redun-
dancy of the dorsal tracheal membrane, or both.
This common description of tracheal collapse represents
FAILURE TO RESPOND an oversimplification of the disease, which has several clini-
The clinician should ask himself or herself the questions cal pictures. Collapse can be the result of a congenital abnor-
listed in Box 21.7 if cats fail to respond to glucocorticoid and mality of small-breed dogs. In many dogs, a congenital
bronchodilator therapy, or if exacerbation of signs occurs predisposition is exacerbated by subsequent inflammatory
during long-term treatment. disease or other exacerbating factors. Collapse can also occur
in dogs of breeds not known to be congenitally predisposed,
Prognosis as a consequence of chronic airway inflammation. Further,
The prognosis for the control of clinical signs of idiopathic the bronchi can be involved along with the trachea or alone,
feline bronchitis is good for most cats, particularly if exten- as the bronchial lumen is normally supported by rafts of
sive permanent damage has not yet occurred. Complete cure cartilage within its walls. In human medicine the term tra-
is unlikely, and most cats require continued medication. Cats cheobronchomalacia (TBM) is used, and TBM is classified
that have severe, acute asthmatic attacks are at risk for further as primary (congenital) or secondary (acquired).
sudden death. Cats with persistent, untreated airway inflam- This terminology more accurately describes the range of
mation can develop the permanent changes of chronic bron- disease observed in dogs and should be adopted by the vet-
chitis and emphysema. erinary profession.
That TBM can have a congenital basis in dogs is sup-
ported by its high prevalence in small-breed dogs. Also,
several studies have demonstrated ultrastructural differences
BOX 21.7 in the tracheal cartilage of toy breed dogs with collapsed
tracheas, compared with those with normal tracheas. Signs
Considerations for Cats With Bronchitis That Fail to may not develop until later in life in many of these dogs.
Respond to Glucocorticoid and Bronchodilator Therapy Presumably, the onset of signs is initiated by an “acute on
chronic” event. An exacerbating problem develops in an
Is the Cat Receiving Prescribed Medication? affected dog, which results in increased respiratory efforts,
Measure plasma theophylline concentrations. airway inflammation, and/or cough. Exacerbating problems
Initiate trial therapy with repositol glucocorticoids.
could include upper airway obstruction, canine infectious
Was an Underlying Disease Missed on Initial Evaluation? respiratory disease complex (CIRDC), heart enlargement or
Repeat diagnostic evaluation, including complete history failure, or parasitic disease, perhaps with contributions from
for potential allergens, thoracic radiographs, tracheal obesity, exposure to tobacco smoke, or poor oral health.
wash fluid analysis, heartworm tests, and fecal Changes in intrathoracic pressures and airway pressures
examinations for parasites. In addition, perform during increased respiratory efforts or cough contribute to
complete blood count, serum biochemical analysis, narrowing of the trachea and stretching of the dorsal liga-
and urinalysis. ment. With severe collapse, fluttering or physical trauma to
Initiate trial therapy with anti-Mycoplasma drug. the mucosa may further stimulate cough. Inflammation also
Initiate trial environmental manipulations to minimize contributes to an ongoing cycle of cough and collapse. Col-
potential allergen and irritant exposure.
lagenases and proteases released by inflammatory cells may
Has a Complicating Disease Developed? weaken the structure of the airways. Damage to the tracheal
Repeat diagnostic evaluation as described in the epithelium and changes in mucus composition and secretion
preceding sections. impair airway clearance. Previously tolerable irritants and
organisms may perpetuate inflammation and cough.