Pulmonary Tuberculosis

Also written as Tuberculosis, pulmonary.

Pulmonary tuberculosis is a contagious infection caused by Mycobacterium tuberculosis, presenting with chronic cough, weight loss, and night sweats. Diagnosis relies on microbiology, imaging, and clinical risk factors. Effective treatment requires multi‑drug therapy and monitoring for drug resistance.

Overview

TB spreads by aerosol droplets and primarily affects the lungs. It is a leading cause of morbidity in low‑resource settings, especially among people with HIV, diabetes, or malnutrition.

• Transmission: airborne droplets
• Incubation: weeks to months
• Typical latency before active disease

Key concepts

Active pulmonary TB is diagnosed when clinical, radiologic, and microbiologic criteria align. Severity is staged by extent of disease on chest X‑ray and sputum burden.

• Diagnostic criteria: compatible symptoms + abnormal CXR + microbiologic confirmation
• Severity: minimal (localized infiltrate) vs extensive (cavitation, bilateral disease)
• Risk groups: HIV, recent contact, immunosuppression, crowded living conditions

Clinical relevance

Prompt recognition prevents transmission and reduces mortality. Untreated disease can cause massive hemoptysis, respiratory failure, or disseminated TB.

• Complications: bronchiectasis, fibro‑cavitary disease, miliary spread
• Immediate threats: massive hemoptysis, acute respiratory distress

Investigations

• Sputum smear microscopy (Ziehl‑Neelsen): Does the patient have acid‑fast bacilli? Positive indicates active TB; negative does not rule out disease.
• Xpert MTB/RIF PCR: Is Mycobacterium tuberculosis present and is rifampicin resistance present? Detects TB quickly and guides therapy.
• Chest X‑ray: What is the pattern of lung involvement? Upper‑lobe infiltrates or cavitation support TB; normal CXR does not exclude early disease.
• Culture (solid or liquid): Is there growth of M. tuberculosis? Gold standard; allows drug‑susceptibility testing but takes weeks.
• HIV test: Is the patient immunocompromised? HIV co‑infection alters presentation and treatment duration.
• If PCR unavailable – use sputum smear + clinical‑radiologic correlation: How to diagnose without molecular test? Rely on smear, CXR, and risk assessment.

Management

Treat with a standard 6‑month regimen of first‑line drugs, monitor adherence, and watch for drug‑resistance or toxicity.

• Initial phase: isoniazid, rifampicin, pyrazinamide, ethambutol – kills actively replicating bacilli and prevents resistance.
• Continuation phase: isoniazid + rifampicin – consolidates cure.
• Avoid monotherapy – selects resistant strains.
• Monitor liver function, vision (ethambutol), and sputum conversion at 2 months.
• If drug‑resistant: refer for second‑line regimen, avoid fluoroquinolones if contraindicated.

Often confused with

Other chronic lung infections and malignancies can mimic TB on imaging and symptoms.

• Non‑tuberculous mycobacterial infection – similar smear but different treatment.
• Lung cancer – weight loss and cough; requires biopsy.
• Chronic fungal infection (e.g., histoplasmosis) – endemic areas, similar CXR.

Where results can mislead

Certain tests may be falsely negative or positive, leading to misdiagnosis.

• Smear negative in HIV patients despite active disease.
• CXR normal in early TB or in immunocompromised hosts.
• Xpert may miss low‑level resistance to drugs other than rifampicin.

Exam pearls

Key points examiners love: linking risk factors, interpreting investigations, and choosing correct drug regimen.

• Always consider HIV status when evaluating TB severity.
• Sputum conversion by 2 months predicts treatment success.
• Rifampicin resistance mandates a different regimen.

Questions an examiner may ask

• A 28‑year‑old HIV‑positive man presents with chronic cough and weight loss – what is your next diagnostic step? — Order sputum Xpert MTB/RIF to confirm TB and detect rifampicin resistance.
• A patient on TB therapy develops visual colour‑vision loss – which drug is responsible and what action is required? — Ethambutol; stop it and replace with a suitable alternative.
• Chest X‑ray shows bilateral upper‑lobe infiltrates in a smoker – how do you differentiate TB from lung cancer? — Obtain sputum for microbiology and consider CT‑guided biopsy if smear negative.
• Why is monotherapy with isoniazid discouraged in latent TB infection? — It rapidly selects resistant mutants; combination therapy is needed for active disease.
• A patient with TB fails to convert sputum after 2 months – what does this indicate? — Possible drug resistance, poor adherence, or extensive disease; reassess regimen and perform susceptibility testing.
• In a resource‑limited clinic without Xpert, how would you diagnose TB? — Use sputum smear, chest X‑ray, and clinical risk assessment; start empiric therapy if suspicion high.
• What are the main causes of mortality in untreated pulmonary TB? — Massive hemoptysis, respiratory failure, and disseminated (miliary) disease.
• How does HIV infection modify the presentation of pulmonary TB? — More likely to have atypical CXR, smear‑negative disease, and rapid progression.

When to seek help

• Massive hemoptysis
• Severe dyspnea or respiratory failure
• Altered mental status

Quick questions

Why is a 4‑drug regimen used initially?

It prevents emergence of resistance by attacking bacilli at different metabolic stages.

Can a negative sputum smear rule out TB?

No; smear sensitivity is low, especially in HIV, so combine with imaging and clinical risk.

What is the role of steroids in pulmonary TB?

Used only for TB meningitis or pericarditis; not routine for uncomplicated pulmonary disease.