Feline Medicine Q&A 11

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The fluid in the bottle has been drained from the pleural space of this 7-year-old neutered male domestic longhaired cat.

Question	Answer		Article
What is this fluid?	The milky appearance of this fluid suggests it is chyle, a chylomicron-rich fluid that has leaked from the thoracic duct. Chylous effusions have a milky-white appearance, although they can be blood-tinged causing a pink (‘strawberry milkshake’) appearance.		Link to Article
What routine laboratory tests would confirm the diagnosis?	Definitive diagnosis of chylothorax is achieved by demonstrating chylomicrons on agar lipoprotein electrophoresis. More practically, comparing chyle with serum reveals triglyceride levels are typically higher in chyle, and cholesterol levels equivalent to or lower in chyle compared with serum. Cytology usually reveals a predominance of mature lymphocytes, and there may be lipid-laden macrophages.		Link to Article
What potential underlying causes should be considered for this cat?	Recognized causes of chylothorax include: Cardiomyopathy/congestive heart failure. Traumatic rupture of the thoracic duct. Anterior mediastinal neoplasia (lymphoma, thymoma). Heartworm disease. Lymphangiectasia. Idiopathic chylothorax: in many cases, an underlying cause is not found.		Link to Article
If additional investigations yielded no specific identifiable cause, what should the approach be to therapy?	Management of idiopathic cases involves initially conservative treatment with repeat thoracocentesis as necessary (possibly via an indwelling chest drain) and reducing the flow of chyle by feeding a low fat diet. Addition of medium chain triglycerides is not recommended; it is questionable whether they are absorbed directly into the circulation (rather than via lymphatics) and their use has been associated with hepatic lipidosis in cats. The benzopyrone derivative, rutin (250–500 mg/cat three times daily, orally), has been recommended, but evidence supporting its efficacy is lacking, and some cases will resolve spontaneously. Where conservative management fails, surgical treatment is recommended with ligation of the thoracic duct. Fibrosing pleuritis can be a long-term complication.		Link to Article