Page 362 - Small Animal Internal Medicine, 6th Edition

334 PART II Respiratory System Disorders

If the described exacerbating factors are sufficiently severe no tracheal collapse, inflammation was identified on BAL
or chronic, even dogs without congenitally weak cartilages and bronchial biopsy, and the presenting cough was described
VetBooks.ir may develop TBM. Of course it is possible that these dogs, as mild and wheezing (Adamama-Moraitou et al., 2012).
Overall, although any signalment is possible, TBM occurs
too, have congenital cartilage abnormalities, imbalances in
their proinflammatory and antiinflammatory mediators, or
Signs may occur acutely but then may slowly progress over
other predisposing factors that as yet are not understood. most commonly in middle-aged toy and miniature dogs.
The clinical consequences of TBM include chronic, pro- months to years. The primary clinical feature in most dogs
gressive cough that can ultimately lead to large airway is a nonproductive cough, described as a “goose honk.” The
obstruction. In some cases the signs of extrathoracic large cough is worse during excitement or exercise, or when the
airway obstruction predominate in the absence of cough. collar exerts pressure on the neck. Eventually (usually after
Most of these dogs develop increased inspiratory efforts with years of chronic cough), respiratory distress caused by
activity or stress, inspiratory stertor, and, eventually, epi- obstruction to airflow may be brought on by excitement,
sodes of hypoxemia. Because the chronic progressive cough exercise, or overheating. Systemic signs such as weight loss,
of TBM is similar to that of chronic airway inflammation anorexia, and depression are not expected.
(e.g., idiopathic chronic bronchitis, eosinophilic broncho- As discussed, some dogs are presented primarily for signs
pneumopathy, bacterial bronchitis, parasitic disease), and of upper airway obstruction without cough, also exacerbated
because TBM can be a consequence of (or coincidental with) during excitement, exercise, or hot weather. Stertorous
these conditions, a thorough and careful diagnostic evalua- sounds may be heard during periods of increased respiratory
tion is essential. efforts.
The prevalence of TBM in dogs is not known. Studies Tracheal collapse in cats is rare and usually secondary to
often originate from referral institutions and may over- another obstructive disease. Careful questioning regarding
represent dogs with poorly responsive signs. In a report of possible trauma and exposure to foreign bodies is indicated.
bronchoscopies performed on 58 dogs, half had some form On physical examination a cough can usually be elic-
of airway collapse (Johnson et al., 2010). Bronchial collapse ited by palpation of the trachea, particularly in those dogs
was reported in 35 of 40 (87.5%) brachycephalic dogs under- presented with cough as the predominant sign. An end-
going bronchoscopy (Delorenzi et al., 2009). We reported expiratory snap or click may be heard during auscultation
findings from 115 dogs with chronic cough, of which 59 as a result of complete intrathoracic collapse. Patients with
(51%) had tracheobronchomalacia (Hawkins et al., 2010). In exercise intolerance or respiratory distress will demonstrate
addition, 31 of 32 (97%) toy-breed dogs had TBM among increased inspiratory efforts and stertorous sounds from col-
their diagnoses. lapse of the extrathoracic trachea, and an audible expiratory
Tracheal collapse is rare in cats and most often occurs wheeze/cough from collapse of the intrathoracic trachea. It
secondary to a tracheal obstruction, such as from a tumor, may be helpful to exercise dogs whose signs are moderate
foreign body, or traumatic injury. or intermittent to identify characteristic breathing patterns
or sounds.
Clinical Features History and physical examination should also emphasize
Tracheobronchomalacia can be primary or secondary and a search for exacerbating or complicating disease. The fre-
can affect the trachea and/or bronchi. More important, from quent association with canine chronic bronchitis has been
a clinical perspective, is that collapse may occur predomi- mentioned. Other possibilities include cardiac disease
nantly in either the extrathoracic (cervical trachea and/or causing left atrial enlargement from mitral valve dysplasia or
thoracic inlet) or intrathoracic (intrathoracic trachea and/or pulmonary edema; airway inflammation caused by bacterial
bronchial) airways. Dogs with predominantly extrathoracic infection, allergic bronchitis, exposure to smoke (e.g., from
tracheal collapse can present with signs of upper airway cigarettes or fireplaces), or recent intubation; upper airway
obstruction, including respiratory distress most pronounced obstruction caused by elongated soft palate, stenotic nares,
on inspiration and audible stertorous sounds. If respiratory or laryngeal paralysis or collapse; and systemic disorders
distress occurs in dogs with intrathoracic airway collapse, it such as obesity or hyperadrenocorticism.
tends to be more pronounced on expiration and is usually
associated with an audible, loud wheeze/cough (Video 21.2). Diagnosis
It is possible that a relationship exists whereby extratho- Tracheobronchomalacia is most often diagnosed on the basis
racic airway collapse is more often associated with primary of clinical signs in conjunction with findings from cervical
(congenital) TBM, and intrathoracic airway collapse is more and thoracic radiography. Radiographs of the neck to evalu-
often associated with secondary (occurring in a predisposed ate the size of the lumen of the extrathoracic trachea are
or nonpredisposed breed) TBM. This conjecture is partially taken during inspiration (Fig. 21.5), when narrowing caused
supported by a study of tidal breathing flow-volume loops in by tracheal collapse is more evident because of negative
toy and small-breed dogs with tracheal collapse and no evi- airway pressure. Conversely, the size of the lumen of the
dence of other respiratory disease, in which abnormalities intrathoracic trachea is evaluated on thoracic radiographs
were seen predominantly in the inspiratory limb (Pardali taken during expiration, when increased intrathoracic pres-
et al., 2010). In a study of 18 dogs with bronchomalacia, but sures make collapse more apparent (Fig. 21.6). Radiographs