Page 378 - Small Animal Internal Medicine, 6th Edition

350 PART II Respiratory System Disorders

fibrosis also requires (1) the exclusion of other known causes
of interstitial lung diseases including domestic and occupa-
VetBooks.ir tional environmental exposures, connective tissue disease,
and drug toxicity; (2) characteristic pattern on high resolu-
tion computed tomography (HRCT) in patients without sur-
gical lung biopsy abnormalities; and (3) specific combinations
of HRCT and surgical lung biopsy lesions in patients with
biopsy. In veterinary medicine, the latter criterion may be
difficult to apply, but attention should be paid to the other
criteria.
Characteristic lesions that result in the histopathologic
pattern of usual interstitial pneumonia are as follows: fibro-
sis, areas of fibroblast proliferation, metaplasia of the alveolar
epithelium, and mild to moderate inflammation. Honey-
comb change may occur as a result of enlarged airspaces A
lined by abnormal alveolar epithelium. The lungs are hetero-
geneously affected, with areas of normal lung intermixed
with abnormal regions. The abnormal regions are often sub-
pleural. A defect in wound healing has been hypothesized as
the cause.
Idiopathic pulmonary fibrosis has been described in cats
on the basis of histologic lesions that are quite similar to
those in people (Cohn et al., 2004; Williams et al., 2006; Fig.
22.3). Unlike the disease that affects people and cats, the
disease in dogs has been associated with the primary lesion
of collagen deposition in the alveolar septa with no fibroblas-
tic foci (Norris et al., 2005).
Neoplasia can occur concurrently with idiopathic pulmo-
nary fibrosis in people and was reported in 6 of 23 cats (Cohn
et al., 2004). The lesions of pulmonary fibrosis can also be B
misinterpreted as carcinoma, and 4 of 23 cats considered to
have pulmonary fibrosis were initially given a pathologic FIG 22.3
diagnosis of carcinoma. Photomicrographs of a lung biopsy from a cat with
idiopathic pulmonary fibrosis. At lower power (A),
Clinical Features distortion and obliteration of the normal pulmonary
architecture are evident because of replacement of the
A breed predisposition is seen in dogs with pulmonary parenchyma with disorganized bands of fibrous tissue and
fibrosis. West Highland White Terriers are most frequently scattered mononuclear inflammatory cells. Few recognizable
reported, with fewer cases documented among Stafford- alveoli can be seen in this section. The alveolar septae are
shire Bull Terriers, Jack Russell Terriers, Cairn Terriers, and thickened, and metaplasia of the alveolar epithelium is
Schipperkes. Both dogs and cats tend to be middle-aged present. At higher power (B), subpleural alveoli show
or older at the time of presentation, although characteris- marked distortion with clear septal fibrosis and type 2
tic signs have been found in patients as young as 2 years epithelial hyperplasia. Although normal areas of the lung
are not shown, the disease is characterized by
of age. heterogeneity of lesions within the lung. (Photomicrographs
Signs are most often slowly progressive over months. In courtesy Stuart Hunter.)
cats the duration of signs may be shorter, with 6 of 23 cats
having shown signs for only 2 days to 2 weeks (Cohn et al.,
2004). Respiratory compromise is the most prominent clini-
cal sign of pulmonary fibrosis, manifested as exercise intoler- Diagnosis
ance and/or rapid, labored breathing. Cough often occurs, Thoracic radiographs of dogs with pulmonary fibrosis typi-
but if it is the predominant sign, higher consideration should cally show a diffuse interstitial pattern. The abnormal densi-
be given to a diagnosis of bronchitis. Syncope may occur in ties generally must be moderate to severe to be distinguished
dogs. from age-related change. A bronchial pattern is often noted
Crackles are the hallmark auscultatory finding in dogs concurrently, contributing to the overlap in signs between
and are noted in some cats. Wheezes are heard in approxi- pulmonary fibrosis and chronic bronchitis. Evidence of pul-
mately half of dogs and in some cats. The abnormal breath- monary hypertension may be seen (see later in this chapter).
ing pattern is typically tachypnea with relatively effortless Radiographs of cats with this disease may show diffuse or
expiration. patchy infiltrate (Fig. 22.4). Patterns may be interstitial,