Detection of Mycobacterium tuberculosis in cervical lymph node with fluorescence microscope and conventional ZN staining at a tertiary care hospital

Background: Tuberculous lymphadenitis is the most common manifestation of extrapulmonary tuberculosis (EPTB), especially in high TB-burden countries like India. It predominantly affects cervical lymph nodes and poses significant diagnostic challenges due to its nonspecific clinical presentation and the paucibacillary nature of the disease. Conventional diagnostic methods such as Ziehl–Neelsen (ZN) staining often have limited sensitivity, particularly in necrotic or low-bacillary-load lymph node samples obtained through fine-needle aspiration cytology (FNAC). These limitations necessitate the evaluation of more sensitive techniques to improve early and accurate diagnosis. Methods: A prospective, cross-sectional study was conducted over 24 months involving 500 patients presenting with clinically suspected tuberculous cervical lymphadenopathy. FNAC was performed, and smears were stained and examined using both ZN and auramine–rhodamine fluorescence techniques. Diagnostic yield, additional case detection, and time efficiency were compared. Results: ZN staining detected AFB in 44.2% (221/500) of cases, whereas fluorescence microscopy identified AFB in 71.6% (358/500), yielding an incremental detection gain of 27.4%. Notably, fluorescence microscopy detected AFB in 30.5% of necrosis-only smears and in 26.2% of cases deemed non-diagnostic by ZN staining. Additionally, fluorescence microscopy reduced the average screening time per smear from 7 minutes to 2.5 minutes. Conclusion: Fluorescence microscopy significantly outperforms conventional ZN staining in detecting Mycobacterium tuberculosis in FNAC samples of head and neck lymphadenitis. Its higher sensitivity, efficiency, and diagnostic utility in challenging smears advocate for its inclusion in standard diagnostic algorithms, particularly in resource-limited, high-TB-burden settings.