PCR detection of Mycobacterium tuberculosis in necrotising non-granulomatous lymphadenitis using formalin-fixed paraffin-embedded tissue: a study in Thai patients

Background: Necrotising non-granulomatous lymphadenitis can be observed in several conditions, most notably infection (including tuberculosis, yersiniosis and nocardiasis), Kikuchi-Fujimoto disease and systemic lupus erythematosus. Aims: To evaluate the role of PCR in the detection of Mycobacterium tuberculosis in necrotising non-granulomatous lymphadenitis in Thai patients using formalin-fixed paraffin-embedded tissue. Methods: 35 patient samples showing necrotising non-granulomatous lymphadenitis were subjected to PCR for detection of the IS6110 sequence of M tuberculosis. For comparison, sections were visually assessed for acid-fast bacilli using the Ziehl-Neelsen stain. Results: Among 35 cases of necrotising non-granulomatous lymphadenitis, a conclusive diagnosis could be reached in 23 cases: 15 cases of Kikuchi-Fujimoto disease, 6 of tuberculosis and 2 of systemic lupus erythematosus. Of the 6 cases of tuberculous lymphadenitis, 4 (66.6%) were detected by PCR in formalin-fixed paraffin-embedded tissue samples. PCR was positive in 6/12 of the remaining cases (50%) in which a definitive diagnosis could not be reached by other methods. Conclusion: Using PCR, a significant percentage (28%) of cases of necrotising non-granulomatous lymphadenitis in this study could be attributed to M tuberculosis. PCR for identification of the organism can be extremely helpful in confirming a diagnosis of tuberculosis when Ziehl-Neelsen staining is negative.