Tuberculosis (TB) - Clinical Features, Investigations & Management

Definition

Clinical Features

Pulmonary TB (most common)

• Chronic cough (>2-3 weeks) - often productive, may be blood-streaked
• Hemoptysis - classic hallmark; occurs from cavity erosion into vessels
• Fever (low-grade, typically evening/night)
• Night sweats
• Progressive weight loss and anorexia
• Pleuritic chest pain (if pleural involvement)
• Dyspnea (if extensive disease or pleural effusion)

• Post-tussive rales in upper lung zones
• Amphoric (hollow) breath sounds if cavitation present
• Signs of consolidation in lower lobes (primary progressive disease)
• Lymphadenopathy is uncommon in immunocompetent adults

Extrapulmonary TB

Constitutional (B-symptoms)

Investigations

1. Sputum Examination (most important)

• Sputum smear (ZN stain / Auramine-Rhodamine): Demonstrates acid-fast bacilli (AFB). Three specimens collected at least 8 hours apart (2 on morning of separate days). ~50% of TB cases can be smear-negative.
• Sputum culture (gold standard): Growth of M. tuberculosis in liquid media (MGIT) within 1-3 weeks; Lowenstein-Jensen (LJ) medium takes 6-8 weeks. Required for drug susceptibility testing (DST).
• Xpert MTB/RIF (GeneXpert): Rapid PCR assay; >95% sensitive/specific for smear-positive sputum; simultaneously detects rifampicin resistance (marker for MDR-TB); ~70% sensitive in smear-negative specimens.

2. Chest X-Ray (CXR)

• Primary TB: Mid/lower lobe consolidation, hilar lymphadenopathy (Ghon complex)
• Reactivation TB: Cavitary lesions in apical and posterior segments of upper lobes (right > left) - classic
• Other findings: Fibrotic scars, loss of lung volume, calcification, "tree-in-bud" opacities (endobronchial spread), miliary pattern
• Ranke complex: Calcified Ghon focus + calcified hilar nodes = healed primary TB

3. Immunological Tests

• Tuberculin Skin Test (TST/Mantoux): Intradermal PPD; read at 48-72h; induration ≥10 mm positive (≥5 mm in HIV+/immunocompromised). Cannot distinguish latent from active TB. False negative in severe TB, HIV, malnutrition.
• Interferon Gamma Release Assay (IGRA): (e.g., QuantiFERON-TB Gold); blood test measuring IFN-γ release to M. tuberculosis antigens (ESAT-6, CFP-10); more specific than TST (not affected by BCG); useful for latent TB diagnosis.

4. Other Investigations

• CBC: Normocytic anemia, lymphocytosis; leukocytosis in severe/miliary disease
• ESR: Elevated (non-specific but correlates with disease activity)
• LFTs: Baseline before starting anti-TB treatment (hepatotoxic drugs)
• HIV testing: Mandatory in all TB patients
• Urine LAM (lipoarabinomannan): Useful in HIV-positive patients with low CD4 count
• Bronchoscopy + BAL / bronchial washings: For smear-negative pulmonary TB
• CT chest: More sensitive than CXR, especially in HIV+ patients with normal CXR; detects cavities, mediastinal nodes, miliary pattern
• FNAC / biopsy: Lymph node, pleural, or tissue biopsy showing caseating granuloma with AFB
• CSF analysis (TB meningitis): Lymphocytic pleocytosis, low glucose, high protein, AFB smear/culture/PCR
• Pleural fluid: Exudate, lymphocyte-predominant; ADA (adenosine deaminase) elevated >40 IU/L is highly suggestive

Management

Principles

• Treat with combination therapy to prevent resistance
• Directly Observed Therapy (DOT) improves adherence
• All isolates should undergo drug susceptibility testing

First-Line Drug-Susceptible TB (standard regimen)

Key Drug Side Effects

Latent TB Treatment

• 3 months of weekly rifapentine + isoniazid (3HP) - preferred
• 4 months of daily rifampicin - alternative
• 6-9 months of daily isoniazid with pyridoxine

Multidrug-Resistant TB (MDR-TB)

• Defined as resistance to at least isoniazid AND rifampicin
• Treat with second-line drugs (fluoroquinolones, bedaquiline, linezolid) for 18-24 months
• Guided by drug susceptibility testing

Monitoring

• Sputum smear/culture at 2 months and end of treatment
• LFTs if symptomatic or high-risk (age >35, HIV, liver disease, alcohol)
• Visual acuity monitoring with ethambutol
• Chest X-ray at baseline and completion

Infection Control

• Respiratory isolation until sputum becomes smear-negative (typically 2-3 weeks of treatment)
• Notify public health authorities (TB is notifiable)
• Contact tracing and screening

1. TB = AFB smear + culture (gold standard) + GeneXpert (fastest)
2. Classic CXR - upper lobe cavitation in reactivation TB
3. 2HRZE / 4HR = standard 6-month regimen
4. Always give pyridoxine with isoniazid
5. Always test for HIV in all TB patients
6. IGRA/TST for latent TB - cannot diagnose active TB alone