The singular case of the pleural effusion

The diagnosis of pleural effusion can present one of the most unique challenges in pulmonary medicine. The mechanisms underlying the accumulation of pleural fluid in health and disease are now well understood. In spite of this the diagnosis of pleural disorders can be problematic, chiefly because the pleural fluid offers relatively limited information for examination. Over fifty different disorders are capable of causing pleural effusions. A needle thoracocentesis can provide a definitive diagnosis (as by the unequivocal demonstration of malignant cells or specific microbes) in only 25 percent of patients. A presumptive diagnosis can be made in an additional 50 percent of patients by piecing together clinical insights. Thus, no more than 75 percent of patients overall are considered to have a conclusive diagnosis at the end of diagnostic workup by pleural fluid analysis alone. The remaining effusions fall into the nebulous category of "undiagnosed pleural effusions and rdquo; and mdash;a wastebasket category for which no universal acceptance exists. The Lights Criteria Rule (and its much-touted abbreviations) have been traditionally used to differentiate transudates from exudates. Criticisms for these rules have been intermittently voiced. Although a fair quantum of clinical judgment is still required in appraising patients with borderline, the Lights Criteria Rule (or its variants) still serves clinicians admirably well.