UNDERSTANDING CHYLE IN CATS

Transcription

1 Vet Times The website for the veterinary profession UNDERSTANDING CHYLE IN CATS Author : DAN FORSTER Categories : Vets Date : February 11, 2008 DAN FORSTER discusses diagnosis and treatment of felines with the potentially fatal disorder chylothorax CHYLE what the hell is that? was my initial response to the arrival of an emergency chylothorax while I was in finalyear rotations at university. This was not a condition that had been extensively covered at university, probably due to its somewhat strange nature and inability to be categorised into a specific lecture. Should it be covered in thoracic surgery (of which I mainly recall making sure I must avoid pinning a cat to the table when inserting a chest drain), or should it, perhaps, be fleetingly covered in clinical pathology when discussing pleural and peritoneal effusions? Then again, maybe cardiovascular medicine would be a better place to inform students of the wonders of this mysterious fluid? In a nutshell, chylothorax is hard to specifically classify. Either way, the aetiology, diagnosis and treatment of this condition make an interesting read. Chyle Chyle is a fluid containing high concentrations of triglycerides (chylomicrons) and lymph. It initially arises from the intestines, which explains the high levels of fat present. Chyle is transported to the venous system by a network of lymphatics in the mesentery, with arborisation in the cisterna chyli a dilated sac adjacent to the aorta at L1-L4. The thoracic duct is the cranial continuation of the cisterna chyli running through the diaphragm 1 / 16

2 and resting between the aorta and azygous vein on the left side of the thorax in cats. Chyle is ultimately deposited (usually) in the left external jugular vein in cats. Chylothorax is an abnormal collection of chyle in the pleural space following leakage from the thoracic duct. Aetiology Anything that causes abnormal flow or pressure in the thoracic duct can potentially cause exudation of chyle from the duct. In these cases the duct is likely to be intact, but dilated, such as in thoracic lymphangiectasia. There may be increased lymphatic flow with or without decreased lymphatic drainage. Any condition that causes increased systemic venous pressures may also cause chylothorax for example, rightsided heart failure, mediastinal neoplasia, CVC thrombi and heartworm, to name the more common ones in cats. Thoracic duct perforation, such as following a road traffic accident, can also cause chyle to leak into the pleural space. These cases, however, are thought to form the minority likely due to the duct s ability to heal rapidly. Often in cats, a direct cause cannot be found; these cases are termed idiopathic chylothorax. The compromised breathing due to pleural effusion, and the debilitating nature of the disease following excessive loss of proteins, fats, vitamins and lymphocytes, all signify this disease as an emergency condition that requires immediate action to correct. The possible presence of underlying ailments, such as heart disease, exacerbates the difficulty in managing this condition. Chronic chylous effusions can also lead to fibrosing pleuritis, due to the irritant nature of the fluid. Unfortunately, this is a terminal condition and, once developed, little can be done. Diagnosis You might think that performing a quick thoracocentesis procedure in a dyspnoeic cat that harbours a milky fluid is sufficient to diagnose chylothorax. However, this is not always the case and further investigation is also required to determine the initial cause of the effusion. Typically, diagnosis is based on physical examination, clinical signs, thoracic radiographs and pleural fluid analysis. Cats are usually dyspnoeic and owners will often report that they have been quiet or off colour for a few days and only recently started breathing heavily. There may also be weight loss and anorexia. Physical examination is variable, but typically demonstrates muffled heart sounds, dyspnoea, increased bronchovesicular sounds, tachycardia and loss of rib spring. Conscious thoracic radiographs (Figures 1a and 1b) can be performed with care and with or without oxygen therapy to confirm the effusion and establish its extent, such as uni or bilateral. 2 / 16

3 Radiographs may also give an idea of heart size, lung pathology, and presence or absence of masses, and can help rule out conditions such as a ruptured diaphragm and pneumothorax. Typical features of a pleural effusion are likely to be observed, including scalloping of lung lobes and an obscured heart shadow. Ultrasonography, echocardiograms and ECGs can be useful to assess the status of the heart and determine whether the animal has a cardiomyopathy. Ruling out the presence of a mediastinal mass is also possible with ultrasound. Blood samples can be taken when cats are more stable. Haematology may demonstrate neutrophilia if there is active inflammation and, possibly, lymphopaenia if lymphocyte loss into the pleural cavity is marked. There may also be low albumin due to protein loss (note that this may be exacerbated by frequent thoracocentesis). Electrolyte disturbances may also be seen, which could relate to dehydration and hypovolaemia. There may also be clues to the initial cause of the effusion for example, eosinophilia may suggest heartworm is playing a part. Cholesterol and triglyceride serum levels should also be assessed and compared to those of the chyle. Additional useful tests may include FeLV/FIV and FIP analysis. Ultimately, pleural fluid analysis following careful thoracocentesis (Figure 2) is required for confirmation of a diagnosis. Chyle has some unique properties that help distinguish it from other fluids. Remember, not all chyle that is tapped from the chest will be fresh, and may take on features of other effusions, so a full analysis is recommended to ensure an accurate diagnosis of 3c Table 1 outlines the main features of chyle. chylothorax (see Figures 3a- ). Treatment If an underlying cause is identified, it should be treated accordingly, such as prescribing heart medication. Once the cause of the chylous effusion is dealt with, the leakage should subside. It is, however, quite common in cats for there to be no obvious cause of the effusion this is known as idiopathic chylothorax. In these cases, it is best to start medical therapy and, if there is no success here, surgery may be indicated. A chest drain should be inserted by routine methods if the effusion continues to recur. However, this is generally only necessary in cases of traumatic duct rupture, which is rare. Repeat thoracocentesis carries risks of iatrogenic damage, and infection and is also stressful for the patient. Preliminary findings suggest that rutin, a benzopyrene extract from fruits of the Brazilian fava d anta tree, appears useful in the management of this condition. It is used widely in human medicine for the treatment of lymphoedema following axillary lymph node excision. The exact mechanism of action is unknown, but rutin is thought to reduce leakage from blood vessels, increase proteolysis and removal of protein from tissues, and enhance macrophage phagocytosis 3 / 16

4 of chyle. Rutin is available over the counter from health food stores. Current recommended dosages are mg/kg orally TID. It comes in both tablet and gel capsule form and can be given as a tablet or mixed with water. (Figures 4 and 5). Studies are required to ascertain the clinical efficacy of this treatment. In animals responding well to initial chest draining and rutin therapy, dietary management can be instigated. Some patients may already be malnourished due to a constant loss of proteins and fats. A balance must be struck to ensure optimum nutritional intake while avoiding the excessive absorption of fats, which will then have to traverse the thoracic duct. This is the next challenge in managing the condition. It was initially proposed that supplementing the diet with medium-chain triglycerides was a good idea since they were thought to bypass the thoracic duct and get absorbed directly by the portal circulation. This has recently been disproved, however, and a low-fat diet is the current recommendation, either commercial (preferred) or home fed. Naso-oesophagael tube feeding, with or without appetite stimulants, may be useful in animals reluctant to eat. Prognosis Poor survival rates are documented with this ailment, regardless of the initial aetiology. Success depends on the presence of other disease conditions causing the chylothorax and the initial response to therapy. A recurrent effusion is harder to manage and the risk of fibrosing pleuritis is higher. Fibrosing pleuritis occurs due to chronic exposure to irritant chyle, which may cause fibrin deposition and connective tissue formation on the pleura. This results in an inability to expand the lungs. Patients that respond well to initial draining and rutin medication are more likely to make a full recovery. However, this is usually a fatal disorder. Animals not responding to medical therapy may need surgical intervention. Cats with severe underlying disease and those that have developed fibrosing pleuritis are not good candidates for surgery and euthanasia should be considered. Options for surgery include mesenteric lymphangiography followed by thoracic duct ligation, pleurodesis and pleuroperitoneal or pleurovenous shunts. None of these techniques has a good success rate and owners should be informed that the chances of a successful outcome are slim. Surgical techniques will not be covered here. Conclusion Chylothorax struck me as an interesting condition that will benefit significantly from further studies. 4 / 16

5 Unfortunately, this disease is as fascinating as it is serious. Animals that are diagnosed promptly and treated for underlying ailments immediately are most likely to recover. 5 / 16

6 6 / 16

7 Figure 1a. Radiographs of a cat with chylothorax. Dorsoventral view Figure 1b. Radiographs of a cat with chylothorax. Lateral chest view. 7 / 16

8 Figure 2. Thoracocentesis being taken from a cat. 8 / 16

9 Figure 3a. The appearance of chyle. Pale, opaque chyle. 9 / 16

10 Figure 3b. The appearance of chyle. Chyle tainted with blood. 10 / 16

11 Figure 3c. The appearance of chyle. A typical milky sample. 11 / 16

12 12 / 16

13 13 / 16

14 Figure 4. Initial findings have suggested that rutin, a natural product that is available over the counter from health stores, is useful in management of chylothorax. 14 / 16

15 Figure 5. Rutin mixed in water for inappetant cats. TABLE 1. Typical features of chyle 15 / 16

16 16 / 16 Powered by TCPDF (