Dyspnea is one of the most common presentations in primary care, as well as one of the most amenable to a structured diagnostic evaluation. Conversely, it is also easy to misdiagnose and mismanage these patients if one employs a haphazard approach.
A careful history plays a key role here, with several factors being of diagnostic value; first among these is the duration of the dyspnea.
Dyspnea which has developed over hours to days (as in this patient) is termed 'subacute' dyspnea; this is most often due to either pulmonary or cardiac disease.
In this respect, key respiratory causes include pneumonia, asthma, and acute exacerbation of chronic obstructive pulmonary disease (COPD); important cardiac etiologies include acute heart failure, myocarditis, and subacute cardiac tamponade.
The presence or lack of associated symptoms is another important factor; pneumonia is clinically less likely in the absence of a cough, while the lack of wheezing is a point against asthma.
medical history is yet another key factor; note that individuals with both asthma and COPD are highly likely to have a positive medical history in this respect.
A detailed examination should follow, with special focus on the general examination, and evaluation of the cardiovascular and respiratory systems.
In this patient, this is highly fruitful, revealing diminished movement of the entire right hemithorax, along with a stony dull percussion note, and diminished vocal resonance; the trachea and apex beat are also deviated to the left.
The above signs are characteristic of a pleural effusion causing a mediastinal shift; while both empyema and hemothorax can also give rise to the same clinical findings, they are significantly less likely, given the absence of symptoms of infection, and lack of antecedent trauma.
A subsequent chest x-ray shows opacification of the right hemithorax with mediastinal shift to the left, strengthening our clinical suspicion.
Thoracentesis is key to her further evaluation; this will confirm the presence of a pleural effusion, and also allow us to establish whether it is transudative or exudative in nature.
Note that exudates are characterized by a serum albumin >35 g/L; they are often unilateral, with pneumonia, tuberculosis, malignancies, pancreatitis, and connective tissue diseases being common causes.
On the other hand, transudates show a serum albumin < 25 g/L; they are usually bilateral, and due to an imbalance between hydrostatic and colloid oncotic forces, as is seen in congestive cardiac failure, cirrhosis, and nephrotic syndrome, among others.
Fortunately, in this patient's case, the highly distinct physical appearance of the aspirate allows us to skip such tedious reasoning; note that the milky-white appearance is suggestive of a chylothorax. This is confirmed by the biochemical analysis revealing triglycerides in the aspirated fluid.
Pseudo-chylothorax is another clinical entity where the aspirated fluid may have such an appearance. However, this is encountered in individuals with longstanding effusions secondary to tuberculosis, rheumatoid arthritis, or connective tissue diseases.
Chylothorax is most often a sequela of thoracic trauma and iatrogenic procedures; however, a significant number of cases are due to neoplasms (particularly lymphoma); further imaging of the thorax via computed tomography (CT) is therefore a must.
Fortunately, the CT scan shows no findings suggestive of a malignancy; thus, given the absence of a clear causative etiology, this is most likely idiopathic chylothorax.
Her management should include reduction of chyle production via a fat-restricted oral diet, and decompression of the pleural space via insertion of an intercostal tube. Note that it is important not to aspirate more than 1.5 liters per day, due to the risk of re-expansion pulmonary edema.
While pleurodesis is a surgical technique used to manage chylothorax, this is mainly preferred if conservative management fails. Furthermore, given the absence of features of infection, there is no rationale for antibiotic therapy - especially since chyle itself is bacteriostatic.
Chylothorax is the accumulation of chyle (a combination of lymphatic fluid with products of fat digestion) in the pleural cavity.
The condition is rare, and most often a sequela of trauma to the thoracic duct; this is frequently iatrogenic (e.g. following thoracic surgery or procedures such as central venous catheterization), but can also occur following penetrating trauma to the thorax, and spinal fractures.
Nontraumatic chylothorax does occur, and may be due to obstruction of the lymphatic flow by extrinsic compression (e.g. tumors), lymphatic duct infiltration by malignancies, or alteration of lymphatic fluid pressure dynamics (for example, in cases of raised central venous pressure or liver cirrhosis).
In one-half of patients, the resultant pleural effusion is right-sided, and in one-third, left-sided. The remainder of cases are bilateral.
The clinical presentation varies, depending on the rate of chyle accumulation in the pleural cavity. Low-volume, slowly growing chylothoraces may be clinically silent, or present with nonspecific symptoms such as dyspnea, cough, and chest discomfort.
On the other hand, a rapid onset, large volume chylothorax may give rise to hemodynamic instability from hypovolemia, and respiratory distress from the mass effect.
Note that chyle is not irritant to the pleura; thus, fever and pleuritic pain are typically absent.
In longstanding chylothoraces, immunodeficiency may result due to immunoglobulin and lymphocyte loss into the pleural cavities. Infection of the chyle itself is rare due to its bacteriostatic properties.
Acute complications include severe hypovolemia and hemodynamic instability (mainly in patients with large volume chylothoraces). Chronic complications include malnutrition, metabolic disturbances such as hyponatremia, acidosis, and hypocalcemia, and opportunistic infections from immunosuppression.
Note in particular that loss of proteins into the pleural fluid can lead to altered activity of drugs which have significant protein binding properties (e.g. digoxin, amiodarone, and cyclosporine)
Plain x-rays of the chest are typically the first diagnostic study, and will show findings suggestive of a pleural effusion in the affected hemithorax.
Thoracentesis is confirmatory; while the pleural fluid is classically described to have a milky white appearance, this is only true in 50% of cases.
Biochemical analysis of the pleural fluid is therefore paramount, with the presence of chylomicrons confirming the diagnosis. In institutions lacking this facility, measurement of pleural fluid cholesterol and triglyceride levels is an alternative.
Note that lymphangiography can be used to assess the site and severity of lymphatic leakage, especially in cases of traumatic chylothorax.
The management of these patients is based on three key principles: conservative management, treatment of any underlying causes, and surgical intervention.
Conservative management aims to reduce the rate of chyle production; it is universally applicable, and the most important component of the management, resolving the condition in roughly half of patients.
This includes appropriate nutrition, and fluid and electrolyte management, including either remaining nil per os (NPO) for short periods or consuming a low-fat, medium-chain triglyceride diet.
If a large volume chylothorax is present, drainage via a chest tube is also important. Medications which reduce the rate of chyle formation, such as somatostatin and octreotide, have also been shown to reduce the severity of the condition.
Where an underlying cause is present this should be treated, e.g. steroids for sarcoidosis or diuretics for heart failure.
Surgical management can be considered in patients with traumatic chylothorax in whom conservative management has failed; another indication, even in patients with non-traumatic chylothorax, is a large volume chylothorax where the daily drainage exceeds 1 to 1.5 liters.
Note that the techniques applicable depend on the clinical setting, available facilities, and expertise of the surgeon; these include ligation of the thoracic duct leak via an open or thoracoscopic approach, pleurectomy, pleurodesis, and pleuroperitoneal shunting.
Interventional radiology offers several alternatives to surgery - specifically percutaneous catheterization and subsequent embolization of the leaking duct. These may be employed in individuals in whom surgery has failed.
1. Chylothorax is a type of pleural effusion, where there is accumulation of chyle in the pleural cavity.
2. Chylothorax can be traumatic or non-traumatic; the former are more common, and are frequently iatrogenic in origin.
3. Thoracocentesis is diagnostic, with biochemical analysis of the aspirated pleural fluid revealing chylomicrons.
4. Conservative management is sufficient in approximately half of all cases.