🦠 Caused by Mycobacterium leprae → an obligate intracellular, aerobic, acid-fast bacillus.
👥 Transmission: mainly human-to-human (likely via respiratory route).
🌱 Chronic granulomatous disease affecting nerves and skin.

🧬 Aetiology

Lives in phagolysosomes of macrophages and vacuoles of Schwann & endothelial cells.
Risk ↑ with age and close contact with infected individuals.
Cannot be cultured in vitro → grows in mouse footpad & nine-banded armadillos.
🐢 Extremely slow growth: doubling time ≈ 13 days.

🌍 Epidemiology

~4 million cases worldwide.
🇮🇳 70% in India; also Brazil, Indonesia, Mozambique, Madagascar, Tanzania, Nepal.

🩺 Clinical Forms

Tuberculoid / Paucibacillary (Strong CMI → elimination of bacilli):
- Incubation: 2–5 years.
- ≤5 skin lesions; usually negative smears.
- Few hypopigmented anaesthetic patches; localised nerve involvement.
Lepromatous / Multibacillary (Weak CMI → uncontrolled bacilli):
- Incubation: 8–12 years.
- ≥6 lesions, skin smear often positive.
- Diffuse papules, nodules → “leonine facies.”
- Nasal discharge sheds bacilli → spreads infection.
- Haematogenous spread to skin, nerves, organs.
- Thickened peripheral nerves (ulnar, median, radial, facial).

🧭 Ridley–Jopling Classification

LL → Lepromatous (low CMI, high bacterial load).
BL → Borderline lepromatous.
BB → Borderline borderline.
BT → Borderline tuberculoid.
TT → Tuberculoid (high CMI, low bacterial load).

🔎 Investigations

Investigation	Details
🧪 Skin Smear	Ziehl–Neelsen stain for AFB from ear lobe/lesion. Positive in multibacillary leprosy.
🔬 Skin Biopsy	Shows granulomas, AFB, nerve changes. Differentiates types of leprosy.
💉 Lepromin Test	Tests CMI response. Positive in tuberculoid; negative in lepromatous. Not diagnostic.
🧬 PCR	Detects M. leprae DNA. Sensitive for paucibacillary disease.
🧠 Nerve Biopsy	Shows granulomas/inflammation. Useful in pure neuritic leprosy.
🧫 Serology	Detects anti-PGL-1 antibodies. Used in multibacillary monitoring.
✂️ Slit-Skin Smear	Provides a bacterial index (BI) → helps monitor severity & treatment.

📋 Summary of Clinical Types

Form	Clinical Features	Management
🟤 Tuberculoid	Few hypopigmented patches, nerve anaesthesia, strong CMI, low bacillary load.	6 months MDT: Rifampicin 600 mg monthly Dapsone 100 mg daily
🔴 Lepromatous	Diffuse lesions, nodules, leonine facies, widespread nerve damage, high bacillary load.	12 months MDT: Rifampicin 600 mg monthly Clofazimine 300 mg monthly + 50 mg daily Dapsone 100 mg daily
🟠 Borderline	Mixed features, variable bacterial load, fluctuating CMI.	Treat as multibacillary (12 months MDT).
🟡 Indeterminate	Early mild disease, few lesions, unpredictable course.	6 months MDT (Rifampicin + Dapsone).

💊 Drugs Used

Drug	Dose (Adults)	Side Effects
Rifampicin	600 mg monthly	Hepatotoxicity, red-orange fluids, flu-like syndrome, thrombocytopenia.
Dapsone	100 mg daily	Haemolysis (esp. G6PD deficiency), methaemoglobinaemia, rash, neuropathy.
Clofazimine	300 mg monthly + 50 mg daily	Skin darkening, ichthyosis, GI upset, photosensitivity.
Ofloxacin	400 mg daily	Tendon rupture (rare), GI upset, CNS effects, photosensitivity.
Minocycline	100 mg daily	Photosensitivity, GI upset, pigmentation, hepatotoxicity (rare).
Clarithromycin	500 mg daily	GI upset, taste disturbance, hepatotoxicity, QT prolongation.
Ethionamide	250–500 mg daily	GI upset, hepatotoxicity, hypothyroidism, neuropathy, depression.

💡 Teaching Pearl: Leprosy spectrum depends on host immunity. Strong CMI → tuberculoid (few lesions, low bacilli). Weak CMI → lepromatous (diffuse, nodules, high bacilli).

The content on this website is provided for educational and informational purposes only to support exam preparation (e.g., MLA, MRCP, USMLE) and learning. This is NOT medical advice, diagnosis, treatment, or professional guidance. It does not replace consultation with a qualified healthcare professional, official guidelines (e.g., NICE, GMC, BNF), or supervised clinical practice. Always verify information with current, authoritative sources. Makindo and its contributors accept no liability for any reliance on this content, including errors, omissions, or any resulting harm, loss, or consequences. By using this site, you agree to these terms.

Leprosy (Hansen’s disease)

📖 About