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Less than 5% of patients with rheumatoid arthritis develop pleural involvement. The effusion can be unilateral or bilateral and a pericardial effusion may also occur in some cases. The cytologic picture is very characteristic.
- Abundant clumps of granular debris
- Macrophages
The abundant granular material can stain green, pink, red or orange with the Papanicolaou stain, and aggregates into irregular clumps. Large, island-like masses can be observed in cell block material. The predominant cell is the macrophage; multinucleated macrophages are seen in most cases. Lymphocytes and polymorphonuclear lymphocytes may be seen. Mesothelial cells are usually absent.