Page 379 - Small Animal Internal Medicine, 6th Edition

CHAPTER 22 Disorders of the Pulmonary Parenchyma and Vasculature 351

A definitive diagnosis of pulmonary fibrosis requires a
lung biopsy obtained by thoracotomy or thoracoscopy. The
VetBooks.ir expense and invasiveness of biopsy preclude its use in some
patients. Furthermore, the lack of specific treatment recom-
mendations for pulmonary fibrosis is a deterrent. However,
biopsy should be considered in patients that are stable and
whose owners have sufficient resources. The less invasive
tests cannot completely rule out the existence of a different,
directly treatable disease (e.g., atypical bacterial infection,
fungal disease, parasitism).
Treatment
Idiopathic pulmonary fibrosis remains a relentless progres-
sive disease even in people (Raghu and Richeldi, 2017). His-
torically, most individuals were treated with prednisone at
low dosages and with azathioprine, as corticosteroids alone
FIG 22.4
Lateral thoracic radiograph from a cat with idiopathic were not considered to be effective. Many other drugs,
pulmonary fibrosis showing a diffuse interstitial pattern with including colchicine, penicillamine, and N-acetylcysteine,
patchy areas of alveolar disease in the caudal lung lobes. have not been proven to be effective. A recent placebo-
Pericardial and mediastinal fat is also seen. Radiographic controlled, prospective study carried out by the Idiopathic
abnormalities in cats with fibrosis are quite variable, Pulmonary Fibrosis Clinical Research Network (2012) found
including the range of interstitial, bronchial, alveolar, or that risks of death and hospitalization were actually increased
mixed patterns.
in patients receiving the combination of prednisone, azathio-
prine, and N-acetylcysteine.
bronchial, alveolar, or mixed but are often quite severe. Bron- Two drugs have been recently approved for the treatment
chiectasis, caused by traction on the airways, may be noted of idiopathic pulmonary fibrosis in people. Nintedanib is an
in either species with advanced disease. antifibrotic drug, and perfenidone has both antifibrotic and
Results of the CBC, serum biochemistry panel, and uri- antiinflammatory properties. Their safety and efficacy in
nalysis are generally unremarkable. Polycythemia may be treating IPF in dogs or cats is not known. Further, these
present secondary to chronic hypoxemia. Screening tests to drugs are prescribed for patients with mild to moderate
identify other causes of interstitial lung disease include fecal disease to slow progression of signs and delay the need for
examinations for parasites, heartworm tests, and appropriate lung transplantation.
infectious disease serology. Most dogs and cats have been treated with corticoster-
Airway specimens should be collected in sufficiently oids and bronchodilators. Theophylline derivatives have
stable patients, primarily to assist in the identification of the theoretical potential to provide some benefit through
other causes of lung disease. Be aware that patients may be potentiation of steroid activity. It is likely that any beneficial
more compromised than they appear to be based on history effect from this combination is actually due to the pres-
and physical examination. Mild to moderate inflammation ence of a steroid-responsive interstitial lung disease (i.e.,
may be seen in patients with pulmonary fibrosis, but this is not idiopathic pulmonary fibrosis) or control of concurrent
a nonspecific finding. Bronchoscopy may be useful in some bronchitis. Animals with signs of pulmonary hypertension
patients for identifying other causes of lung disease, such as are treated for this complication, as described later in this
chronic bronchitis. chapter. Omeprazole may be beneficial, particularly for
Typical lesions identified by computed tomography are patients receiving steroids. In people, gastroesophageal reflux
often used in making a presumptive diagnosis of idiopathic is common with idiopathic pulmonary fibrosis, and micro-
pulmonary fibrosis in people. Similar lesions can be seen in aspiration is speculated to play a role in the pathogenesis of
some dogs with the disease (Johnson et al., 2005; Heikkila the disease. Hypoxemia and corticosteroid administration
et al., 2011). Results of computed tomography in cats have can make patients more prone to adverse gastrointestinal
not been reported. effects (Heikkila-Laurila and Rajamaki, 2014).
Although not yet commercially available, measurement
of serum endothlin-1 (ET-1) shows promise as a diagnostic Prognosis
test for idiopathic pulmonary fibrosis in dogs. In a study The prognosis for idiopathic pulmonary fibrosis in dogs and
that included dogs with idiopathic pulmonary fibrosis, cats is poor, with relentless progression of disease expected.
chronic bronchitis, or eosinophilic bronchopneumopathy, Nevertheless, individual patients, particularly dogs, can
and healthy Beagle dogs, serum ET-1 concentrations greater survive for longer than a year. The mean survival time in
than 1.8 pg/mL had a sensitivity of 100% and a specificity dogs in one study was 18 months from the onset of signs,
of 81% for the diagnosis of idiopathic pulmonary fibrosis with survival up to 3 years (Corcoran et al., 1999). The prog-
(Krafft et al., 2011). nosis in cats is poorer. Of 23 cats, 14 died or were euthanized