Page 333 - Small Animal Internal Medicine, 6th Edition

CHAPTER 20 Diagnostic Tests for the Lower Respiratory Tract 305

diagnosis. The finding of intracellular bacterial organisms in eosinophilia, usually as part of a mixed inflammatory
cytologic preparations without evidence of oral contamina­ response.
VetBooks.ir tion indicates the presence of infection. The growth of any terized by the finding of increased numbers of activated
Macrophagic (granulomatous) inflammation is charac­
of the systemic mycotic agents in culture is also clinically
significant, whereas the growth of bacteria in culture may or
inflammation, along with increased numbers of other
may not be significant because low numbers of bacteria can macrophages, generally present as a component of mixed
be present in the large airways of healthy animals. In general, inflammatory cells. Activated macrophages are vacuolated
the cytologic identification of bacteria and their growth in and have increased amounts of cytoplasm. This response is
culture without multiplication in enrichment broth are sig­ nonspecific unless an etiologic agent can be identified.
nificant findings. Lymphocytic inflammation alone is uncommon. Viral or
Bacteria that are not seen cytologically and that grow only rickettsial infection, idiopathic interstitial pneumonia, and
after incubation in enrichment media can result from several lymphoma are considerations.
situations. For example, the bacteria may be causing infec­ True hemorrhage can be differentiated from a traumatic
tion without being present in high numbers because of the specimen collection by the presence of erythrophagocytosis
prior administration of antibiotics, or because of the collec­ and hemosiderin­laden macrophages. An inflammatory
tion of a nonrepresentative specimen. The bacteria may also response is also usually present. Hemorrhage can be caused
be clinically insignificant and represent normal tracheal by neoplasia, mycotic infection, heartworm disease, throm­
inhabitants, or they may result from contamination during boembolism, foreign body, lung lobe torsion, or coagulopa­
collection. Other clinical data must therefore be considered thies. Evidence of hemorrhage is seen occasionally in animals
when such findings are interpreted. with congestive heart failure or severe bacterial pneumonia.
The role of Mycoplasma spp. in respiratory disease of the Of note is that hemosiderosis is found in tracheal wash fluid
dog and cat is not well understood. These organisms cannot collected from cats with a wide range of diseases, including
be seen on cytologic preparations and are difficult to grow idiopathic bronchitis.
in culture. Specific transport media are necessary. Growth of
Mycoplasma organisms from tracheal wash fluid may indi­
cate primary or secondary infection or may be an insignifi­ NONBRONCHOSCOPIC
cant finding. Testing for Mycoplasma by PCR is also available. BRONCHOALVEOLAR LAVAGE
Treatment is generally recommended if inflammation was
documented cytologically. Indications and Complications
Criteria of malignancy for making a diagnosis of neopla­ Nonbronchoscopic bronchoalveolar lavage (NB­BAL) is
sia must be interpreted with extreme caution. Overt charac­ considered for the diagnostic evaluation of patients with
teristics of malignancy must be present in many cells in the lung disease involving the interstitium, small airways, or
absence of concurrent inflammation for a definitive diagno­ alveoli that are not tachypneic or otherwise showing signs of
sis to be made. respiratory distress (see Table 20.2). This author prefers tra­
The type of inflammatory cells present in tracheal wash cheal wash for patients with diffuse airway disease, bacterial
fluid can assist in narrowing the differential diagnoses, bronchopneumonia, or aspiration pneumonia because tra­
although a mixed inflammatory response is common. Neu­ cheal wash carries less risk and can be expected to result in
trophilic (suppurative) inflammation is common in bacterial a representative specimen in these situations. Further,
infections. Before antibiotic therapy is initiated, the neutro­ NB­BAL using a catheter for dogs as described in the follow­
phils may be (but are not always) degenerative, and organ­ ing text will usually sample a caudal lung lobe and could
isms can often be seen. Neutrophilic inflammation may be a bypass the exudate from pneumonia of airway origin. There­
response to a variety of other diseases. For instance, it can fore NB­BAL is considered primarily for patients with diffuse
be caused by other infectious agents or seen in patients with interstitial lung disease. Bronchoscopically guided BAL is
canine chronic bronchitis, idiopathic pulmonary fibrosis, or performed as a routine part of bronchoscopy and is indicated
other idiopathic interstitial pneumonias, or even neoplasia. when focal disease is present.
Some cats with idiopathic bronchitis have neutrophilic A large volume of lung is sampled by BAL (Figs. 20.20
inflammation rather than the more classic eosinophilic and 20.21). The collected specimens are of large volume,
response (see Chapter 21). The neutrophils in these instances providing more than adequate material for routine cytology,
are generally nondegenerative. cytology involving special stains (e.g., Gram stains, acid­fast
Eosinophilic inflammation reflects a hypersensitivity stains), multiple types of cultures (e.g., bacterial, fungal,
response, and diseases commonly resulting in eosinophilic mycoplasmal), or other specific tests that might be helpful in
inflammation include allergic bronchitis, parasitic disease, particular patients (e.g., flow cytometry, PCR). Cytologic
and eosinophilic lung disease. Parasites that affect the lung preparations from BAL fluid are of excellent quality and
include primary lungworms or flukes, migrating intestinal consistently provide large numbers of well­stained cells for
parasites, and heartworms. Over time, mixed inflammation examination.
can occur in patients with hypersensitivity. It is occasionally Although general anesthesia is required, the procedure is
possible for nonparasitic infection or neoplasia to cause associated with few complications in stable patients. The