[A case of pulmonary tuberculous initially diagnosed as sarcoidosis because of necrotizing granuloma].

A 75-year-old man with diabetes mellitus visited our hospital because of a chest radiograph abnormality. He was asymptomatic, and no abnormality was detected by blood tests including QuantiFERON-TB Gold (QFT-2 G); hence we conducted a follow-up examination. In 8 months, his chest radiography and CT findings worsened despite remaining asymptomatic. He was admitted for further tests. Analysis of bronchoalveolar lavage fluid (BALF) showed normal results for total cell counts and lymphocytes, but the CD4/8 ratio increased, and bacterial examination yielded negative results. Surgical lung biopsy showed an epithelioid cell granuloma with fibrinoid necrosis and Langhans giant cells, and some bacilli were positive for acid-fast stain. At this point, we suspected sarcoidosis, necrotizing granulomatosis, and mycobacterosis. However, the mycobacterial culture from the lung tissue was positive, and it was identified as Mycobacterium tuberculosis. We diagnosed pulmonary tuberculosis. Even if QuantiFERON-TB Gold In-Tube (QFT-3 G) for active tuberculosis is negative, it may yield false negative results in individuals in an immunosuppressed state and low CD4 count. When we suspect pulmonary tuberculosis from radiographic and pathological findings, we should consider the results of QFT-2 G and QFT-3 G carefully as an adjunct to the diagnosis of tuberculosis.