Page 372 - Clinical Small Animal Internal Medicine

340 Section 4 Respiratory Disease

anorexia, lethargy, and/or dyspnea. Although more of pleural effusion, diagnostic test results may not be
VetBooks.ir common in young animals, pyothorax can occur at any reflective of disease and a nonseptic exudate may be seen.
Many feline pyothorax infections are due to multiple
age, with rare reports in neonatal dogs and cats.
Additional clinical signs include weight loss, nasal or
pyothorax include Pasteurella spp., Clostridium spp.,
ocular discharge, hypersalivation, coughing, and exercise organisms and common bacterial isolates in feline
intolerance. Clinical signs can be acute or chronic. Fusobacterium spp., Bacteroides spp., Peptostreptococcus
Physical examination findings often include tachypnea, anaerobius, Porphyromonas spp., Prevotella spp., and
dyspnea, decreased ventral lung sounds, muffled heart Actinomyces spp. In dogs, enteric organisms are more
sounds, and restrictive respiratory pattern. Severe sepsis common than in cats and common bacterial iso-
and associated signs could occur in either species, with lates include Escherichia coli, Enterobacter cloacae,
pyothorax being the most common cause in a retrospec- Pasteurella spp., Actinomyces spp., Streptococcus canis,
tive paper on cats with severe sepsis. Peptostreptococcus anaerobius, Bacteroides spp.,
In dogs, causes include bite wounds, penetrating Fusobacterium spp., and Porphyromonas spp. Additional
thoracic injury, foreign body inhalation, lung abscess, clinicopathologic findings seen in patients with pyothorax
parasitic migration, hematogenous spread, esophageal or include elevated liver enzymes, electrolyte disturbances,
tracheal perforation, diskospondylitis, neoplasia with hypoglycemia or hyperglycemia, hypoalbuminemia, mild
lung abscessation, previous thoracic surgery, and thora- anemia, and leukocytosis due to neutrophilia.
cocentesis. In cats, causes include extension from a lung Imaging techniques include thoracic ultrasound, radi-
parenchymal infection, foreign body migration, esopha- ographs, and CT. In clinical practice, thoracic ultrasound
geal rupture, and penetrating thoracic wounds. Cats with is typically utilized initially because it is noninvasive,
pyothorax are 3.8 times more likely to live in multiple cat does not require sedation, and can be used rapidly in
households, Pasteurella spp. are the most common bac- patients with respiratory disease for diagnosis and to
terial isolate, and 14.5–40% of cases have a history of bite localize an area for therapeutic thoracocentesis. With
wounds, thus adding support to the theory that bite pyothorax, pleural fluid is often echogenic and wispy,
wounds are a common route of infection. Migrating fibrinous strands can be seen along pleural margins.
grass awns can be a common cause of pyothorax in dogs Radiographs may be helpful once fluid has been removed
and cats, depending on geographic location, but in many to determine if an underlying cause can be identified,
cases the cause of infection is not identified. such as a lung mass lesion, focal pulmonary opacity, or
Diagnosis is based on presence of an exudate, cytologic foreign body; however, as previously mentioned, an
slide evaluation, and positive bacterial cultures of asepti- underlying cause is rarely found. The use of CT is becom-
cally collected pleural fluid. Intracellular bacteria identi- ing more widespread in veterinary medicine but the role
fied on cytologic review confirms the diagnosis but if of CT in canine pyothorax is controversial. A retrospec-
intracellular bacteria are not seen and degenerate neutro- tive study in dogs with spontaneous pyothorax showed
phils are present, then bacterial cultures (aerobic and that common CT findings include bilateral pleural fluid,
anaerobic) should be performed (Figure 34.3). If the pleural gas (due to preimaging thoracocentesis or thora-
patient has already been on antibiotics prior to collection costomy tube placement), pleural thickening, pulmonary
parenchymal abnormalities, and mediastinal involve-
ment. Of the surgically managed dogs in this study, CT
correctly predicted the extent of disease in only 62.5%
and correctly identified the underlying cause in only
50%; therefore, surgical exploration remains the gold
standard to identify underlying pathology.
Treatment includes administration of appropriate
antimicrobials, intermittent or continuous thoracic
drainage, thoracic lavage, and surgery. Intravenous
broad‐spectrum antimicrobials with adequate anaerobic
coverage should be started once culture samples have
been collected and adjusted accordingly based on culture
and susceptibility results. Potentiated beta‐lactams are
reasonable first‐line therapy because they have efficacy
Figure 34.3 Pyothorax cytology. Pyothorax in a dog with a against Actinomyces spp., anaerobes, and some gram‐
predominance of mature, mildly karyolytic neutrophils that negative organisms. Enrofloxacin is often added to
sometimes contain bacilli or coccobacilli forms (Wright‐Giemsa
stain, 100× objective). Source: Photo courtesy of Sarah S.K. Beatty, improve gram‐negative coverage while awaiting culture
DVM, University of Florida. results. Deescalation of antimicrobial therapy should be