Application of a paraffin-embedded pleural effusion cell block to detect mycobacteria : A case of Mycobacterium goodii pleuritis.

The diagnosis of pleuritis caused by mycobacteria is not always easy. Ziehl-Nielsen staining utilizing cell blocks (CBs) of lower respiratory samples was reported to be useful in the diagnosis of pulmonary tuberculosis. However, CBs of pleural effusion (PE) are not commonly used in the differential diagnosis of benign pleuritis. A 100-year-old woman was transferred to our emergency department due to respiratory failure. The patient had massive right PE and an elevated serum carbohydrate antigen 125 level, but no tumor lesions were identified. Mycobacterial examinations using the usual procedures for PE did not lead to a definitive diagnosis. However, Ziehl-Nielsen staining detected several accumulations of acid-fast bacilli in paraffin-embedded PE-CB sections. Finally, sequence analysis of the 16S rRNA gene using the remaining PE-CB showed high homology (99.79%) to that of Mycobacterium goodii. This case suggests that analysis of PE-CBs may be useful for diagnosing suspected cases of mycobacteria-induced pleuritis with negative acid-fast bacilli smears for PE. J. Med. Invest. 72 : 202-206, February, 2025.