Tuberculosis

🌍 Tuberculosis (TB) remains a leading global cause of infectious death. 🧪 Always test for HIV in TB patients. 💉 BCG protects mainly against severe childhood TB (meningitis, miliary). 📋 TB is a notifiable disease in the UK.

🔬 Microbiology

• Mycobacterium tuberculosis = obligate aerobe, acid-fast bacillus (Ziehl–Neelsen stain → 🔴 red rods).
• Cell wall: lipid-rich (mycolic acids) → acid-fastness + survival in macrophages.
• ⏱️ Slow-growing: generation time 12–18h (vs. <30 min for E. coli).
• 🧪 Cord factor: drives granuloma formation.
• Lab ID: Niacin & nitrate reduction positive.

🌍 Epidemiology & Risk

• ~2 billion people infected worldwide; ~3 million deaths annually.
• UK: common in migrants (Sub-Saharan Africa, Indian subcontinent), homeless, alcohol misuse, HIV.
• 📈 Rising with HIV (CD4 <200 → ↑ reactivation/extrapulmonary risk).
• 💊 MDR-TB = isoniazid + rifampicin resistance. 💊 XDR-TB = MDR + fluoroquinolone + ≥1 injectable resistance.

🫁 Clinical Types

• Primary TB: Ghon focus + regional LN = Ghon complex. Often silent.
• Latent TB: Dormant bacilli. TST/IGRA positive, no symptoms.
• Post-primary (reactivation): Apical cavitation, haemoptysis, weight loss, night sweats.
• Miliary TB: Haematogenous spread → millet-seed lesions 🌾 in lungs/other organs.
• Extrapulmonary TB: – 🧠 CNS: meningitis, tuberculoma, Pott’s spine. – 🚻 GU: sterile pyuria, infertility. – 🍽️ GI: ileocaecal mass, obstruction. – ❤️ Cardiac: pericarditis → constrictive. – 🧂 Adrenal: Addison’s disease.

📋 Clinical Features

• 🗣️ Cough >3 weeks ± haemoptysis.
• 🌡️ Fever, night sweats, weight loss (“consumption”).
• 😮 Chest pain, breathlessness if pleural involvement.
• ⚠️ Extrapulmonary clues: meningism, back pain, sterile pyuria.

🔎 Investigations

• 🩸 Sputum AFB smear: Ziehl–Neelsen stain; ≥2 positive = highly infectious.
• 🧫 Culture: Löwenstein–Jensen agar (gold standard, 4–8 wks).
• 🧪 NAAT (GeneXpert MTB/RIF): Rapid, detects rifampicin resistance.
• 💉 TST/Mantoux: Induration ≥5–15 mm depending on risk group.
• 🧬 IGRA: Detects latent TB; not affected by BCG.
• 📷 Imaging: – CXR: apical cavitation (post-primary), hilar LN (primary), miliary nodules (<5 mm). – CT/MRI: CNS/spine/disseminated TB.
• 🔬 Histology: Caseous granulomas + Langhans giant cells.

💊 Management (Drug-Sensitive TB)

• Standard 6-month regimen: – 2 months: Isoniazid + Rifampicin + Pyrazinamide + Ethambutol (HRZE). – 4 months: Isoniazid + Rifampicin (HR).
• 👁️ Directly Observed Therapy (DOT) → improves adherence.
• 💊 Steroids: CNS/pericardial TB (reduce inflammation).

💊 Drug Toxicities (High-Yield)

• 💊 Isoniazid → hepatitis, neuropathy (give pyridoxine).
• 🟠 Rifampicin → hepatitis, orange secretions, P450 inducer.
• 🔥 Pyrazinamide → hepatitis, hyperuricaemia/gout.
• 👁️ Ethambutol → optic neuritis (red–green colour blindness).
• 👂 Streptomycin → ototoxic + nephrotoxic.

⚠️ Drug-Resistant TB

• 🧬 MDR-TB: Needs fluoroquinolone + injectable ± newer agents (bedaquiline, linezolid).
• 💊 XDR-TB: MDR + fluoroquinolone + ≥1 injectable resistance.
• ⏳ Duration: 18–24 months.

🤝 TB & HIV

• 📷 CXR often atypical (lower/mid zones, no cavitation).
• CD4 <200 → more extrapulmonary TB.
• Mantoux often negative (anergy).
• 🧪 Start ART within 2–8 weeks of TB treatment (watch for IRIS).
• ⚠️ Rifampicin → P450 inducer → ART interactions.

🧪 Key Exam Pearls

• 📌 Primary TB = Ghon focus + nodes = Ghon complex.
• 🌾 Miliary TB = millet-seed pattern on CXR.
• 🦴 Pott’s disease = vertebral TB with cold abscess.
• 🧬 IGRA = latent TB, not affected by BCG.
• 💨 Most infectious: smear-positive pulmonary TB.
• 🧪 Always ask about HIV, immunosuppression, travel, BCG history.