Lipoprotein analysis in a chyliform pleural effusion: implications for pathogenesis and diagnosis

A chyliform effusion is an uncommon high lipid pleural effusion that does not result from a leakage of the thoracic duct. Characteristically, it emerges from chronic pleurisy and contains high levels of cholesterol. The origin of this cholesterol is unknown, but it is often attributed to the degeneration of red and white blood cells. In this study we have carried out detailed lipoprotein analyses in a chyliform effusion, a chronic tuberculous effusion and three inflammatory effusions of recent onset, in an attempt to elucidate the process of cholesterol accumulation and possible lipoprotein alterations. Mean cholesterol was 92 mg/dl in the inflammatory exudates and 1,237 mg/dl in the chyliform effusion. In inflammatory effusions of recent onset most cholesterol was bound to low density lipoprotein (LDL) with corresponding apoprotein B levels. The chronic tuberculous exudate showed a shift of cholesterol binding towards high density lipoprotein (HDL). In the chyliform effusion most cholesterol was found in the HDL region. Our results suggest that in acute inflammation, the pleural barrier opens to plasma LDL. We hypothesize that in chronicity this cholesterol becomes trapped in the pleural space and undergoes a change in lipoprotein binding characteristics. In a chyliform effusion, cholesterol further accumulates and builds complexes containing triglycerides and proteins. In clinical routine, total cholesterol values above 200 mg/dl strongly suggest a chyliform effusion. Since triglyceride values may be as high as in chylous effusions (greater than 110 mg/dl), the diagnostic routine in all suspected high lipid effusions should involve cholesterol and triglyceride measurements.