What are the diagnostic approaches for tuberculosis (TB) of the lymph nodes?

From the Guidelines

Diagnosing lymph node tuberculosis (TB) requires a combination of clinical evaluation, imaging studies, and microbiological confirmation, with fine needle aspiration cytology (FNAC) and endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) being recommended diagnostic tests 1. The diagnostic approach typically begins with a thorough physical examination to identify enlarged lymph nodes, most commonly in the cervical region. Ultrasound, CT scan, or MRI may be used to visualize the affected lymph nodes, showing characteristic features such as matting, necrosis, or hypoechoic areas.

• FNAC is often the first invasive diagnostic procedure, providing material for cytology, acid-fast bacilli (AFB) staining, and culture.
• If FNAC is inconclusive, excisional or incisional lymph node biopsy may be necessary to obtain tissue for histopathological examination, which typically shows granulomatous inflammation with caseous necrosis.
• Microbiological confirmation through culture remains the gold standard, though it takes 2-8 weeks for results.
• Newer molecular tests like GeneXpert MTB/RIF provide rapid detection of Mycobacterium tuberculosis and rifampicin resistance within hours, as suggested by the European Union standards for tuberculosis care 1.
• Interferon-gamma release assays (IGRAs) or tuberculin skin tests can support the diagnosis by indicating TB infection, though they cannot distinguish between active and latent infection. In resource-limited settings where advanced diagnostics are unavailable, empiric treatment may be initiated based on clinical presentation and basic investigations, following the official American Thoracic Society/Centers for Disease Control and Prevention/Infectious Diseases Society of America clinical practice guidelines 1.

From the Research

Diagnostics for Lymph Node TB

• The diagnosis of lymph node tuberculosis (TB) can be achieved through various methods, including Cartridge-based Nucleic Acid Amplification Test (CBNAAT) 2, polymerase chain reaction (PCR) 3, imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) 4, and excisional biopsy 5.
• CBNAAT has been shown to be a rapid diagnostic tool with high sensitivity (93.42%) and specificity (86.96%) for lymph node TB 2.
• PCR has also been evaluated for the diagnosis of lymph node TB, with a sensitivity of 58.2% and specificity of 93.9% 3.
• Imaging techniques such as CT and MRI can be used to detect lymphadenopathy and characterize the infection as active or not 4.
• A systematic review of diagnostic pathways for tuberculous lymphadenitis recommended the use of Xpert Mycobacterium tuberculosis/RIF, which has high sensitivity and specificity, but is more expensive than other tests 6.
• Excisional biopsy is a common diagnostic approach for lymph node TB, with 60.4% of cases in one study being managed with a combination of surgical excision and anti-tubercular treatment (ATT) 5.

Diagnostic Test Characteristics

• CBNAAT: sensitivity 93.42%, specificity 86.96% 2
• PCR: sensitivity 58.2%, specificity 93.9% 3
• Xpert Mycobacterium tuberculosis/RIF: high sensitivity and specificity, but more expensive than other tests 6

Clinical Considerations

• Lymph node TB can present with single or multiple enlarged lymph nodes, with cervical lymph nodes being the most commonly affected 5.
• The diagnosis of lymph node TB should be considered in patients with risk factors such as HIV infection or AIDS 5.
• Early diagnosis and treatment of lymph node TB are crucial to prevent complications and improve outcomes 2, 6, 5.