Page 374 - Clinical Small Animal Internal Medicine

342 Section 4 Respiratory Disease

that increased pressure causes chyle to leak out of dilated
VetBooks.ir lymphatics, as would occur in other parts of the body
with lymphedema. With cardiac disease, chylous effusion
can develop due to impaired lymph drainage to the
venous circulatory system. In addition, hepatic conges-
tion occurs with heart failure, which significantly
increases hepatic lymph production and therefore
thoracic duct flow. Pathophysiologic mechanisms for
idiopathic chylous effusion are not well elucidated.
Chylothorax can occur in any breed or age of dog or
cat, with Afghan hounds being overrepresented because
of the association between lung lobe torsion and chylo-
thorax. Clinical signs are those typical of pleural effu-
sions, including lethargy, hyporexia or anorexia, weight
loss, tachypnea, cough, and paradoxical or restrictive
breathing pattern. Diligent cardiothoracic auscultation Figure 34.4 Chylothorax cytology. Chylothorax in a cat consisting
should be performed because of the association between of a mixture of mostly mature small, well‐differentiated
cardiac disease and chylothorax. Additional physical lymphocytes and intermediate‐sized lymphocytes. One
examination findings include muffled heart sounds, lymphocyte has smudged chromatin (top, right), a sign of partial
decreased ventral lung sounds, and increased dorsal lung degradation (Wright‐Giemsa stain, 50× objective). Source: Photo
sounds. There are no consistent laboratory findings for courtesy of Sarah S.K. Beatty, DVM, University of Florida.
dogs or cats with chylothorax.
Diagnosis of chylothorax is based on examination of trolytes and removal of large quantities of chylous
pleural fluid, which grossly appears milky white to effusion can cause hypovolemia, hyponatremia, hyper-
opaque pink‐white, but can vary depending on nutri- kalemia, hypoproteinemia, lymphopenia, weight loss,
tional status of the patient. Pleural fluid from thoraco- and immunosuppression. Conservative medical treat-
centesis should be saved in EDTA for cytologic ment involves pleural evacuation and nutritional
examination and a serum separator tube for triglyceride management. Surgical treatment for idiopathic chylous
concentration analysis. The fluid is most often classified effusion involves ligation of the thoracic duct with or
as an exudate, but may be classified as a modified transu- without various adjunctive procedures including subto-
date depending on the protein and cell count. Cytologic tal pericardectomy, cisterna chyli ablation, and thoracic
examination shows predominantly lymphocytes, small omentalization.
numbers of macrophages, and nondegenerate neutro- Diets low in fat have been recommended for medical
phils, which increase in numbers with chronicity of management of chylothorax in dogs and cats to decrease
pleural effusion (Figure 34.4). the volume of chyle production and therefore flow
Definitive diagnosis is made by demonstrating higher through the thoracic duct; however, this has not been
triglycerides in pleural fluid than in serum samples, experimentally validated in dogs or cats. Rutin is a com-
collected at the same time. If the effusion triglyceride mercially available benzopyrone nutritional supplement
concentration is >100 mg/dL, chylomicrons are seen used in humans for treating lymphedema and commonly
microscopically on a wet‐mount preparation, pleural cho- recommended for medical management of idiopathic
lesterol concentration is less than serum cholesterol con- chylothorax, although no proven beneficial effects have
centration, or Sudan stain verifies lipid in the sample, then been demonstrated in dogs and cats. Theoretical benefi-
it is also classified as chylous. Once the diagnosis of chy- cial actions of rutin include edema uptake by lymphatic
lothorax has been made, additional diagnostics, including vessels, reduction of blood vessel permeability, and
complete blood count, chemistry profile, heartworm test, enhancement of tissue macrophage number and function
thoracic radiographs, thoracic ultrasound, echocardio- to promote phagocytosis of protein in chylous fluid.
gram, thoracic CT, +/− abdominal imaging, should be Octreotide, a somatostatin analogue, inhibits biliary, pan-
considered to determine if an underlying disease can be creatic, and gastric secretions, and is recommended in
found. Cats should also be tested for retroviral diseases. humans with chylothorax to decrease thoracic duct flow;
Treatment of chylothorax should be directed at the however, use in dogs and cats requires further research.
underlying disease but as the disease is often idiopathic, Prior to surgical treatment, some form of thoracic
targeted treatment is rarely possible. Resolution of res- duct imaging is typically recommended to allow for
piratory distress by removing the pleural effusion should surgical planning given the anatomic variation within
be initial treatment, regardless of etiology. Chylous and between species. Mesenteric lymphangiography, or
effusion is rich in lymphocytes, protein, lipid, and elec- the use of aqueous contrast material injected into a