Dermatology, Venereology and Leprosy
Leprosy
Leprosy for MBBS and NEET-PG: Mycobacterium leprae, Ridley-Jopling spectrum, WHO classification, slit-skin smear, lepra reactions and multidrug therapy, mapped to NMC codes DR9.
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Leprosy
Leprosy for MBBS and NEET-PG: Mycobacterium leprae, Ridley-Jopling spectrum, WHO classification, slit-skin smear, lepra reactions and multidrug therapy, mapped to NMC codes DR9.
Leprosy is a defining subject of Indian dermatology and a high-yield examination topic. This chapter covers Mycobacterium leprae and the Ridley-Jopling spectrum, the WHO classification for treatment, the cardinal signs and nerve involvement, the slit-skin smear, the type 1 and type 2 reactions, and WHO multidrug therapy with its adverse effects.
High-yield: Leprosy
- Leprosy is a chronic granulomatous infection caused by Mycobacterium leprae, an obligate intracellular acid-fast bacillus that cannot be grown on artificial media.
- It has a predilection for cooler parts of the body and for peripheral nerves and skin, sparing warm areas such as the axilla, groin and scalp.
- The Ridley-Jopling spectrum runs from tuberculoid, with strong cell-mediated immunity, through borderline forms to lepromatous, with poor immunity and a high bacillary load.
- The WHO operational classification for treatment is paucibacillary, up to five skin lesions and a negative smear, and multibacillary, six or more lesions or a positive smear.
- The cardinal signs are a hypopigmented anaesthetic patch, thickened peripheral nerves and a positive skin smear for acid-fast bacilli.
- Tuberculoid leprosy shows few well-defined anaesthetic patches with early nerve thickening, whereas lepromatous leprosy shows many symmetrical lesions with nodules and few sensory changes.
- A leonine facies with loss of the lateral eyebrows, madarosis, is a feature of advanced lepromatous disease.
- Commonly thickened nerves include the ulnar, common peroneal, posterior tibial, great auricular and radial cutaneous nerves.
- The slit-skin smear samples dermal fluid to demonstrate acid-fast bacilli and calculate the bacterial index for classification and monitoring.
- Type 1 (reversal) reaction is a delayed hypersensitivity flare with inflamed lesions and worsening nerve function, and is treated with corticosteroids to prevent nerve damage.
- Type 2 reaction, erythema nodosum leprosum, is an immune-complex reaction of lepromatous disease with crops of painful nodules, fever and systemic upset, treated with steroids or thalidomide.
- WHO multidrug therapy for multibacillary leprosy is rifampicin, clofazimine and dapsone; paucibacillary disease uses rifampicin and dapsone.
- Clofazimine causes a reversible reddish-brown skin discolouration, and dapsone can cause haemolysis, especially in G6PD deficiency.
- Deformities such as claw hand, foot drop and trophic ulcers arise from nerve damage, so early treatment of reactions is the key to preventing disability.
Leprosy: spectrum and reactions
- **Cardinal signs:** Hypopigmented anaesthetic patch, thickened nerve, positive slit-skin smear.
- **WHO classification:** Paucibacillary up to 5 lesions; multibacillary 6 or more or smear positive.
- **Type 1 reaction:** Delayed hypersensitivity, inflamed lesions and nerve damage; steroids.
- **Type 2 (ENL):** Immune complex, painful nodules and fever in lepromatous disease; steroids, thalidomide.
NMC competencies in this chapter
- **DR9.1:** Classification, epidemiology, aetiology and microbiology of leprosy
- **DR9.2:** Clinical features and classification of leprosy
- **DR9.3:** Indications and performance of the slit-skin smear
- **DR9.4:** Lepra reactions and their supportive management
- **DR9.5:** Pharmacology of drugs used in leprosy
- **DR9.6:** Treatment of leprosy based on WHO guidelines
- **DR9.7:** Complications of leprosy and their management
Frequently Asked Questions
What are the cardinal signs of leprosy?
A hypopigmented patch with loss of sensation, thickened peripheral nerves, and a slit-skin smear positive for acid-fast bacilli. The presence of any one of these supports the diagnosis.
How is leprosy classified for treatment?
The WHO operational classification divides it into paucibacillary, up to five skin lesions with a negative smear, and multibacillary, six or more lesions or a positive smear, which determines the drug regimen.
What is the difference between type 1 and type 2 lepra reactions?
Type 1 is a delayed hypersensitivity reversal reaction with inflamed lesions and nerve damage. Type 2, erythema nodosum leprosum, is an immune-complex reaction of lepromatous disease with painful nodules and fever.
What is the WHO multidrug therapy for leprosy?
Multibacillary disease is treated with rifampicin, clofazimine and dapsone, and paucibacillary disease with rifampicin and dapsone, for defined durations that eliminate the infection and prevent resistance.
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