Page 330 - Clinical Small Animal Internal Medicine

298 Section 4 Respiratory Disease

The cough is usually described as harsh and “gagging” disease can lead to respiratory distress that resembles
VetBooks.ir and results from activation of bronchial cough receptors signs of severe asthma on initial evaluation. Plasma
levels of N‐terminal pro‐brain natriuretic peptide (NT‐
by inflammatory debris, mucus, and smooth muscle
spasm. Inhalation of mechanical or chemical irritants
tive heart failure and primary respiratory disease in cats
can trigger cough, leading to the sporadic nature of the proBNP) can be used to differentiate between conges-
clinical signs. Further, acute exacerbations may be with acute dyspnea when specific cut‐off values are
observed in patients with chronic signs, which can result used. Parasitic bronchitis caused by Aelurostrongylus
in periodic wheezing or dyspnea in patients with a long‐ abstrusus, Capillaria aerophila, Paragonimus kellicotti,
standing history of occasional cough. Clinical signs ref- or pulmonary migration of Toxocara cati is character-
erable to the upper airways, including sneezing, nasal ized by eosinophilic lower airway inflammation and can
discharge, and stertor, have been anecdotally reported in be associated with clinical signs that mimic chronic
asthmatic cats. In fact, histopathologic inflammatory manifestations of asthma. Heartworm‐associated res-
changes have been documented in the nasal passages of piratory disease complex should also be considered a
cats with experimentally induced asthma. Inspiratory differential diagnosis for feline bronchial asthma.
stridor and dyspnea associated with dynamic upper air- Specific testing (i.e., Baermann fecal examination, fecal
way obstruction have also been described in an asth- flotation, heartworm antibody testing) should be per-
matic cat. Signs of systemic illness, including inappetence, formed to exclude these conditions before a diagnosis of
lethargy, and depression, are not typically reported. feline asthma is reached.
Physical examination findings in asthmatic cats are Laboratory abnormalities seen with feline asthma are
likewise variable. Due to the intermittent nature of the nonspecific but can include a peripheral eosinophilia,
clinical signs, physical examination may yield no abnor- occurring in 20–57% of patients. A peripheral neutro-
malities. Alternatively, observation of the respiratory philia can also be noted in moderately to severely affected
pattern may reveal an end‐expiratory “push” as air cats. Hyperproteinemia due to hyperglobulinemia may
trapped within the lungs following inspiration is develop consequent to chronic inflammation. Results of
forcefully expelled through narrowed airways during serum biochemistry analysis are typically unremarkable.
expiration. In severely affected patients, air trapping can Thoracic radiography is standardly employed in the
lead to lung hyperinflation, resulting in decreased diagnostic evaluation of suspected asthmatics. However,
compliance of the thoracic wall and, subsequently, a thoracic radiography should not be solely relied upon for
“barrel‐shaped” appearance to the thorax. Tachypnea diagnosis, as findings can be variable and nonspecific.
with prolongation of the expiratory phase may be A bronchial pattern is most commonly seen, consistent
observed at rest. Resistance to airflow caused by reduced with airway inflammatory infiltrates. Interstitial, alveolar,
intraluminal airway diameter results in turbulence, and mixed patterns have also been documented in asth-
which is exhibited clinically as wheezing that may be matic patients. Consolidation of the right middle lung
audible with or without a stethoscope. Inspiratory crack- lobe may be observed and results from obstruction of the
les, increased bronchial sounds, and/or rhonchi may also bronchus by mucus plugging that preferentially occurs in
be identified on thoracic auscultation, or no abnormal this lung segment due to its perpendicular orientation to
sounds may be appreciated. In some patients, palpation the mainstem bronchus. Hyperinflation of the lungs,
of the trachea elicits cough. Stress associated with identified by flattening of the diaphragm, is also consist-
restraint can greatly exacerbate the clinical signs. ent with asthma. Importantly, no pulmonary abnormali-
ties may be detected in as many as 25% of cases.
Bronchoscopy provides additional information that
Diagnosis can be used to support a diagnosis of feline asthma. The
most common bronchoscopic finding identified in cats
In human patients, asthma is definitively diagnosed on with lower airways disease is airway obstruction by
the basis of pulmonary function testing such as spirom- mucus. Nodular irregularities of the epithelium, airway
etry that requires a voluntary expiratory maneuver. Since hyperemia, static or dynamic airway collapse, and
such maneuvers are not feasible in feline patients, there bronchial stenosis are also frequently seen. As with radi-
remains at present no gold standard diagnostic test by ography, these findings are not specific for feline asthma.
which feline asthma is diagnosed. Complications ranging from hemoglobin desaturation to
Currently, clinical diagnosis relies on compatible clin- pneumothorax have been documented in up to 24% of
ical signs, pathology noted on thoracic radiography, cats undergoing bronchoscopy. Pretreatment with terb-
airway cytology abnormalities, and exclusion of other utaline has been associated with a lower incidence of
causes of similar findings. In an acute setting, condi- these complications. When the necessary precautions
tions such as congestive heart failure and pleural space are taken, bronchoscopy can be performed safely in