Diagnosis: Rheumatoid pleural effusion
• The photomicrograph shows three characteristic features seen in rheumatoid effusions: necrotic debris and degenerated cells (lower left portion of photo); multinucleated giant cells; and elongated, spindle- or carrot-shaped epithelioid cells that are histiocytes and thus are cytokeratin negative. The slender epithelioid histiocytes may resemble so-called “snake” cells seen in squamous cell carcinoma.
• Squamous carcinomas occasionally involve serous surfaces, and they can shed single tadpole-shaped cells. Usually, malignant cells in clusters also are present.
• The clinical history combined with the triad of necrotic material, epithelioid spindle cells, and multinucleated giant cells favor a rheumatoid effusion. Immunocytochemical staining may be helpful for diagnostic confirmation and correlation with clinical laboratory findings is also important.
• Necrosis and multinucleated giant cells are uncommon findings in tuberculous effusions. Tuberculous effusions typically contain numerous lymphocytes and rare or no mesothelial cells.
• Rheumatoid effusions are almost always unilateral and are almost always pleural. Pericardial and peritoneal rheumatoid effusions are rare.
