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Tuberculosis

SNOMED: 56717001952 words•Updated 03/03/2026
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Exam Tips

  • Always distinguish latent TB (asymptomatic, non-infectious) from active TB (symptomatic/progressive; infectious if pulmonary/laryngeal).
  • For finals/OSCEs, state the core diagnostic triad: microbiological confirmation (smear/culture/PCR), imaging, and HIV testing with baseline safety bloods.
  • Remember standard adult drug-susceptible regimen: 2 months HRZE then 4 months HR, with pyridoxine alongside isoniazid.
  • In viva questions, highlight rifampicin interactions (including contraception failure risk) and ethambutol visual toxicity monitoring.
  • Think extrapulmonary TB in persistent constitutional symptoms plus site-specific features (nodes, meninges, spine, GU, pericardium).
  • Image spotters: apical cavitation or miliary nodules on CXR are classic high-yield findings (See Figure: apical cavitary TB; See Figure: miliary TB pattern).

Definition

Tuberculosis (TB) is a communicable infection caused by the Mycobacterium tuberculosis complex, most often affecting the lungs but capable of involving almost any organ system. In UK practice, it is classified as active TB (symptomatic/progressive disease, potentially infectious if pulmonary or laryngeal) or latent TB infection (immune sensitisation without clinical disease, symptoms, or infectivity), with later reactivation risk.

Pathophysiology

Inhaled droplet nuclei containing M. tuberculosis reach terminal airways and alveoli, where bacilli survive in macrophages by inhibiting intracellular killing. A Th1-cell mediated immune response (notably IFN-gamma) drives granuloma formation with caseous necrosis, containing organisms in many people (latent infection) but not sterilising them. Active disease develops when bacillary replication outpaces host control (primary progression or reactivation), causing tissue destruction, cavitation, and haematogenous/lymphatic spread to extrapulmonary sites (for example meninges, spine, lymph nodes, pericardium). See Figure: granuloma with central caseation and peripheral epithelioid histiocytes/Langhans giant cells; See Figure: upper-lobe cavitating pulmonary TB on chest radiograph.

Risk Factors

  • Close contact with an infectious pulmonary/laryngeal TB case (especially household exposure, poor ventilation, prolonged contact)
  • Birth in or long residence in high-incidence countries (>40/100,000 per year); in England many cases occur in non-UK-born populations
  • HIV infection and other immunosuppression (including anti-TNF therapy such as infliximab, chemotherapy, prolonged high-dose corticosteroids, post-transplant states)
  • Chronic kidney disease (especially renal replacement therapy), diabetes mellitus, silicosis, haematological malignancy, malnutrition
  • Previous untreated/inadequately treated TB or poor adherence to prior TB therapy
  • Age under 5 years (higher risk of severe/disseminated disease)
  • Social deprivation, homelessness, imprisonment, alcohol misuse, injecting drug use, smoking

Clinical Features

Symptoms

  • Persistent cough (typically >3 weeks), sputum production, possible haemoptysis
  • Fever, drenching night sweats, weight loss, anorexia, fatigue
  • Pleuritic chest pain or breathlessness in pulmonary disease
  • Painless cervical lymphadenopathy (extrapulmonary TB)
  • Back pain or neurological symptoms in spinal TB
  • Headache, vomiting, confusion, meningism in TB meningitis
  • Urinary symptoms, abdominal pain, or altered bowel habit depending on extrapulmonary site

Signs

  • Cachexia, pyrexia, tachycardia
  • Crackles/bronchial breathing over affected lung zones; signs of pleural effusion
  • Cervical or other peripheral lymph node enlargement
  • Focal neurological deficits or reduced consciousness in CNS disease
  • Spinal tenderness/kyphotic deformity in vertebral involvement
  • May be minimal signs early; latent TB has no examination findings

Investigations

Sputum acid-fast bacilli (AFB) smear microscopy:May show acid-fast bacilli; positive smear suggests higher infectivity but does not confirm species or sensitivities
Mycobacterial culture (sputum or site-specific sample):Definitive diagnosis with species identification and drug susceptibility testing; results may take weeks
Nucleic acid amplification test (NAAT/PCR) for TB complex:Rapid confirmation of M. tuberculosis complex and early rifampicin resistance signal in some assays
Chest X-ray:Classically upper-zone infiltrates/cavitation; may show miliary nodules, pleural effusion, or fibrotic change
CT thorax (if needed):Defines cavitation, nodules, tree-in-bud change, lymphadenopathy, and complications
IGRA (or Mantoux in selected settings):Supports latent TB diagnosis (immune sensitisation) but cannot distinguish latent from active disease
HIV test and baseline bloods (FBC, U&E, LFTs, CRP/ESR):Detects comorbidity/co-infection and provides safety baseline before treatment
Site-specific sampling (for example lymph node biopsy, CSF, pleural fluid, ascitic fluid, urine):Granulomatous inflammation/caseation, positive culture/PCR, and organ-specific evidence of TB

Management

Lifestyle Modifications

  • Notify TB to public health and involve specialist TB services early
  • Infectious pulmonary/laryngeal TB: respiratory isolation initially, cough hygiene, and contact tracing
  • Adherence support (including directly observed therapy where indicated), social support, and harm-reduction measures
  • Screen and manage comorbidities (especially HIV, diabetes, malnutrition, alcohol/drug dependence)

Pharmacological Treatment

Drug-susceptible active TB (adult first-line regimen)

  • Isoniazid 300 mg once daily
  • Rifampicin 600 mg once daily (or 10 mg/kg, max 600 mg)
  • Pyrazinamide 20-25 mg/kg once daily (commonly 1.5-2 g once daily by weight band)
  • Ethambutol 15 mg/kg once daily

Standard course is 2 months HRZE then 4 months HR (specialist-directed variations exist). Add pyridoxine (vitamin B6) 10 mg daily with isoniazid to reduce peripheral neuropathy risk, especially in diabetes, alcohol dependence, HIV, malnutrition, pregnancy, or CKD.

Latent TB infection (specialist/public health protocols)

  • Isoniazid 300 mg once daily plus rifampicin 600 mg once daily for 3 months
  • Or isoniazid 300 mg once daily for 6 months

Use risk-stratified UK regimens and check interactions before rifampicin-containing therapy. Exclude active TB before latent treatment to avoid monotherapy of active disease.

Key safety warnings and contraindication-focused prescribing points

  • Isoniazid: risk of hepatitis and peripheral neuropathy
  • Rifampicin: potent enzyme inducer (major interactions; reduces efficacy of combined oral contraceptives, warfarin, many antiretrovirals)
  • Pyrazinamide: hepatotoxicity and hyperuricaemia/gout flare risk
  • Ethambutol: optic neuritis risk (reduced visual acuity/red-green discrimination)

Obtain baseline and interval LFTs; monitor visual symptoms and consider baseline visual acuity/colour vision before ethambutol. Use caution or avoid hepatotoxic regimens in significant liver disease and adjust strategy with specialist input. Counsel that rifampicin discolours urine/tears orange and can stain contact lenses. Manage MDR-TB only with specialist multidrug regimens guided by susceptibilities.

Surgical / Interventional

  • Drainage of large tuberculous pleural effusion or empyema when clinically indicated
  • Neurosurgical/orthopaedic decompression or stabilisation for spinal TB with cord compromise
  • Pericardiocentesis/pericardial window for haemodynamically significant tuberculous pericardial effusion

Complications

  • Ongoing transmission to contacts from untreated infectious pulmonary/laryngeal disease
  • Drug-resistant TB (including MDR-TB) after inadequate or poorly adhered treatment
  • Post-TB chronic lung disease (bronchiectasis, airflow obstruction/COPD phenotype, fibrotic destruction, aspergilloma in residual cavities)
  • Respiratory failure or cor pulmonale after extensive pulmonary damage
  • Disseminated or CNS TB with neurological disability
  • Psychosocial harm, stigma, anxiety, and social isolation
  • Death (risk markedly higher if diagnosis is delayed, untreated, or with HIV co-infection)

Prognosis

With prompt diagnosis, susceptibility-guided treatment, and good adherence, outcomes are usually favourable in drug-susceptible TB. Untreated active TB is often slowly progressive but can be fatal over years; mortality is much higher in smear-positive disease, in older patients, with extensive disease, HIV co-infection, and in drug-resistant TB. Prognosis worsens with delayed diagnosis and social barriers to treatment completion.

Sources & References

💊BNF Drug References(2)

✅NICE Guidelines(1)

📖Textbook References(5)

  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1743, 1744)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1744)[context]
  • David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 594)[context]
  • [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 588, 589)[context]
  • [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 627, 628)[context]

Sources

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