Tuberculous (TB) Lymph Node - Investigations & Treatment

Overview

Stages of TB Lymph Node (Pathological)

Investigations

Routine / Baseline

• CBC with differential - lymphocytosis may be seen; anemia in chronic disease
• ESR/CRP - elevated, markers of systemic inflammation
• Mantoux (TST) - positive (>10 mm in immunocompetent; >5 mm in HIV) - indicates exposure/sensitization, not active disease
• LFT + RFT - mandatory pre-treatment (rifampicin and isoniazid are hepatotoxic; pyrazinamide raises uric acid; streptomycin is nephrotoxic)
• HIV serology - all TB patients; alters management
• Blood sugar / HbA1c - rule out DM as comorbidity
• Uric acid - baseline before pyrazinamide

Imaging

Cytological / Histological (Key Diagnostic Tests)

1. FNAC (Fine Needle Aspiration Cytology)

• First-line diagnostic test for peripheral lymphadenopathy
• Cytomorphological patterns:
  • Epithelioid granulomas with or without caseation
  • Langhans giant cells
  • Caseous necrosis - most characteristic
• Sensitivity: 47-67%; good specificity
• All FNAC aspirates must be sent for: cytology + ZN stain + culture + CBNAAT (Xpert MTB/RIF)

2. CBNAAT / Xpert MTB/RIF (GeneXpert)

• Recommended by Index-TB Guidelines (India) as an adjunct to FNAC
• Detects M. tuberculosis DNA + rifampicin resistance simultaneously in ~2 hours
• PMID 39130352 confirms CBNAAT as an "emerging expert" in head and neck TB diagnosis
• Higher sensitivity than ZN stain for pauci-bacillary EPTB
• Identifies rifampicin resistance - guides MDR-TB treatment

3. ZN Stain (Ziehl-Neelsen) / AFB Smear

• Simple, cheap, rapid - detects acid-fast bacilli
• Low sensitivity in EPTB (pauci-bacillary disease)
• Fluorescence microscopy (FM) has greater sensitivity but requires special equipment

4. Culture on Lowenstein-Jensen (LJ) Medium

• Gold standard for confirmation + drug sensitivity testing (DST)
• Takes 6-8 weeks; BACTEC/MGIT system faster (2-3 weeks)
• Mandatory for DST in all cases

5. Excision Biopsy

• Indicated when:
  • FNAC is inconclusive
  • Malignancy suspected (lymphoma)
  • Atypical mycobacteria suspected
  • No response to ATT
• Sends specimen for: histopathology + Xpert + microscopy + culture
• Do NOT do incisional drainage - risk of chronic fistulization

6. Histopathology

• Caseating granulomas with Langhans giant cells = hallmark
• ZN stain on sections for AFB
• PAS stain to exclude fungal etiology

7. Molecular / PCR

• TB-PCR / Line Probe Assay (LPA) - rapid, detects drug resistance
• Used when CBNAAT is unavailable or for second-line DST

Treatment

Antitubercular Therapy (ATT)

First-Line Regimen

Total duration: 6-9 months

• Standard uncomplicated TB lymph node: 6 months
• Cases with bone involvement, extensive disease, HIV, or poor initial response: 9 months

Drug Doses (Adult)

Pre-Treatment Assessment (Mandatory)

• LFT (transaminases) - H and R are hepatotoxic
• RFT + uric acid - Z and S are nephrotoxic; Z causes hyperuricemia
• Ophthalmology review - E causes optic neuritis (color vision + visual acuity)
• HIV status, blood sugar

Monitoring During Treatment

• Monthly clinical review: node size, sinus healing
• LFT at 2 weeks then monthly for first 2 months
• Chest X-ray at completion

Paradoxical Reaction

• Nodes may enlarge or new nodes appear 2-3 months into treatment
• Due to immune reconstitution - does NOT mean treatment failure
• Managed with NSAIDs; steroids occasionally if severe
• Steroids have no established role in routine TB lymph node treatment (Index-TB Guidelines)

Surgical Treatment

Key surgical principle: Avoid incisional drainage of TB/atypical mycobacterial nodes - it leads to chronic fistulization. Aspiration is preferred for fluctuant nodes.

Differential Diagnosis (to exclude)

• Reactive lymphadenitis (viral - EBV, CMV)
• Lymphoma (Hodgkin's and Non-Hodgkin's)
• Metastatic carcinoma
• Sarcoidosis (non-caseating granulomas, elevated ACE)
• Atypical mycobacteria (NTM)
• Cat-scratch disease (Bartonella henselae)
• Syphilis (VDRL/RPR)
• Toxoplasmosis (immunocompromised)

MDR-TB Lymph Node

• Rifampicin resistance detected on CBNAAT/Xpert = presumed MDR-TB
• Refer to MDR-TB treatment centre
• Second-line regimens per DST results (bedaquiline, linezolid, levofloxacin-based)
• Duration: typically 18-20 months (or shorter with newer all-oral regimens)

Key Points for Surgery Exams

1. FNAC is the first-line investigation - send for cytology + AFB + CBNAAT + culture
2. CBNAAT (Xpert MTB/RIF) is recommended in all FNAC specimens - detects rifampicin resistance
3. Excision biopsy when FNAC inconclusive or malignancy suspected
4. Never do incisional drainage of TB/NTM nodes - causes fistula
5. Standard ATT regimen: 2HRZE + 4RHE = 6 months (extend to 9 months for complications)
6. Nodes not responding to ATT after adequate trial = excise
7. Paradoxical enlargement during ATT is not treatment failure
8. Pre-treatment assessment of LFT, RFT, vision (ethambutol), uric acid, HIV is mandatory