Page 717 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

692 CHAPTER 3

VetBooks.ir Aetiology/pathophysiology Clinical presentation
In the acute stage of disease, signs may include fever,
The most common organisms associated with pneu-
monia include Streptococcus zooepidemicus or other
low pattern, exercise intolerance, nasal discharge
beta-haemolytic Streptococcus spp., which can be depression, increased respiratory rate with a shal-
complicated with infection by gram-negative bacte- and intermittent coughing. Other signs may include
ria such as Pasteurella spp., Escherichia coli, Enterobacter rapid weight loss, sternal and/or limb oedema and
spp., Klebsiella spp. and Pseudomonas spp. Anaerobes gait stiffness, and horses may stand with abducted
such as Bacteroides spp. and Clostridium spp. may also be elbows due to pleural pain that can be elicited by pal-
involved but are less common. Mycoplasma felis has been pation of the thoracic wall. Signs may be mistaken
identified as an additional cause of pleuritis in horses. for colic or laminitis. In chronic pleuropneumonia,
Pleuropneumonia may occur spontaneously, but signs may be limited to intermittent fever, weight
common risk factors include recent transportation, loss and exercise intolerance.
viral infection, oesophageal obstruction (choke)
or general anaesthesia. Bacterial pleuropneumo- Differential diagnoses
nia results from exudative fluid accumulation in the Other infectious pneumonias, including viral, fun-
pleural cavity in response to inflammation and infec- gal, parasitic or even heaves, should be considered.
tion. As large amounts of fluid containing bacteria, Primary lung neoplasia is uncommon, but thoracic
neutrophils, fibrin and cellular debris accumulate in lymphoma or metastatic tumours such as squamous
the thoracic cavity, layers of fibrin develop over the cell carcinoma (SCC) may be considered as differen-
visceral and parietal pleura. Adherence of visceral tial diagnoses for the presence of pleural fluid.
and parietal pleura by fibrin leads to loculation of
fluid, as well as the development of an inelastic fibrin Diagnosis
membrane over the pleural surfaces that may limit History, clinical signs and physical examination are
lung expansion within the thoracic cavity during usually suggestive. Careful auscultation of the thorax
respiration. may detect even subtle abnormalities in early disease,
including crackles or wheezes, decreased lung sounds
in the ventral lung field, mucus movement within the
trachea and/or pleural friction rubs. Bilateral chest
percussion is essential and helps to determine both
3.149 the presence and amount of pleural fluid within each
hemithorax. A pain response may be elicited during
percussion in acute cases. An inflammatory leuco-
gram (neutrophilia, may include band neutrophils)
and hyperfibrinogenaemia are common.
Thoracic ultrasonography is the preferred diag-
nostic tool for characterisation of pleural fluid
(Fig. 3.149). Consolidated or atelectatic lung may
also be visible depending on its location. The entire
field of both lungs should be assessed to detect any
abscesses, loculation of fibrinous fluid or adhesions; to
provide important information regarding prognosis;
and to monitor response to treatment over time.
Thoracocentesis is indicated to further charac-
Fig. 3.149 Transthoracic ultrasonography of a terise the pleuropneumonia, to isolate organism(s)
horse with pleuropneumonia reveals the presence of involved and as a therapeutic measure (Fig. 3.150).
pleural effusion (labelled EFF) between the parietal Cytological examination of pleural fluid with
and visceral pleura in the left hemithorax. A similar Gram staining for bacterial organisms should be
effusion was detected in the right hemithorax. performed. Increased cellularity of pleural fluid