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Introduction & Microbiology - Ancient Affliction

  • Causative agent: Mycobacterium leprae (Hansen's bacillus).
  • Acid-fast, obligate intracellular bacillus; rod-shaped.
  • Slow generation time: 12-14 days.
  • Optimal growth temperature: 27-33°C (cooler body areas).
  • Reservoirs: Humans, nine-banded armadillos.
  • Transmission: Primarily respiratory droplets; prolonged close contact.
  • Long incubation period: Avg 2-5 years (up to 20 years).

Mycobacterium leprae is an obligate intracellular parasite that cannot be cultured on artificial media.

Mycobacterium leprae bacteria with acid-fast staining

Classification - Spectrum Story

Leprosy is a spectrum based on host Cell-Mediated Immunity (CMI).

  • Ridley-Jopling (R-J) Spectrum:

    • Tuberculoid (TT): ↑CMI, few bacilli. Well-defined lesions, early nerve damage.
    • Lepromatous (LL): ↓CMI, many bacilli. Diffuse lesions, late nerve damage.
    • Borderline (BT, BB, BL): Intermediate, unstable forms.
  • WHO Classification (Treatment):

    • Paucibacillary (PB):5 skin lesions AND smear negative. (Mainly TT, BT).
    • Multibacillary (MB): >5 skin lesions OR smear positive OR >1 nerve involved. (Mainly LL, BL, BB).

Leprosy Classification Diagram

⭐ CMI is strongest in Tuberculoid (TT) leprosy (few bacilli, localized) and weakest in Lepromatous (LL) leprosy (many bacilli, disseminated).

Clinical Features - Nerve & Skin Tales

  • Skin Lesions ("Patches & Plaques")
    • One/more hypopigmented or reddish skin patches.
    • Definite sensory loss (touch, pain, temperature) within patches.
    • Plaques, nodules; skin can be shiny, dry, or thickened.
    • Late: Madarosis (eyebrow/eyelash loss), leonine facies (LL).
  • Nerve Damage ("Silent Sabotage")
    • Thickened, often tender, peripheral nerves (e.g., ulnar, common peroneal, great auricular).
    • Sensory loss: Fine touch, pain, temperature affected early.
    • Motor loss: Muscle weakness, paralysis leading to deformities (e.g., claw hands, foot drop, lagophthalmos).
    • Autonomic dysfunction: Anhidrosis (reduced sweating), dry/cracked skin.

Leprosy manifestations: facial lesions, skin, nerve

⭐ The ulnar nerve is the most commonly affected peripheral nerve in leprosy, followed by the common peroneal nerve.

Diagnosis - Unmasking Hansen's

  • Slit-Skin Smear (SSS):
    • Sites: Earlobes, active lesions. Ziehl-Neelsen (ZN) stain for Acid-Fast Bacilli (AFB).
    • Bacteriological Index (BI): Measures bacillary load, graded 0 to 6+.
    • Morphological Index (MI): Percentage of solid, uniformly stained (viable) bacilli; MI ↓ with effective treatment.
  • Histopathology (Biopsy): Confirms diagnosis & classifies leprosy type (e.g., granuloma structure, lymphocyte infiltration, bacillary presence).
  • Nerve Biopsy: Useful in pure neuritic leprosy when skin lesions are absent.
  • PCR: Detects M. leprae DNA; high sensitivity, especially in paucibacillary (PB) or early cases.

⭐ The Lepromin test (Fernandez and Mitsuda reactions) is negative in lepromatous leprosy (LL, BL) and positive in tuberculoid leprosy (TT, BT), indicating Cell-Mediated Immunity (CMI) status. Mycobacterium leprae in a slit skin smear

Management & Reactions - Healing & Hazards

  • MDT Regimens (WHO):
    CategoryDrugsDuration
    PBRifa (600mg M) + Dap (100mg D)6 mo
    MBRifa (600mg M) + Dap (100mg D) + Clofa (300mg M, 50mg D)12 mo
    SLPBSDR: Rifa (600mg) + Oflox (400mg) + Mino (100mg)Single
  • Lepra Reactions: MDT always continued.

⭐ Thalidomide is drug of choice for severe Type 2 lepra reaction (ENL) but is strictly contraindicated in pregnancy due to teratogenicity.

High‑Yield Points - ⚡ Biggest Takeaways

  • Caused by Mycobacterium leprae; primarily affects skin and peripheral nerves.
  • Spectrum: Paucibacillary (PB) (strong CMI, e.g., TT) to Multibacillary (MB) (poor CMI, e.g., LL).
  • Cardinal signs: anesthetic skin lesions, thickened peripheral nerves, positive slit-skin smear (MB).
  • Lepra Reactions: Type 1 (Reversal, cell-mediated) and Type 2 (ENL, immune complex).
  • Treatment: WHO Multidrug Therapy (MDT) with Rifampicin, Dapsone, Clofazimine.
  • Nerve damage is the hallmark, leading to significant disability and deformity.

Practice Questions: Leprosy

Test your understanding with these related questions

Asymmetrical nerve thickening with several hypoesthetic macules on skin indicates which stage of leprosy:

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Flashcards: Leprosy

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Which type of leprosy shows satellite lesions?_____

TAP TO REVEAL ANSWER

Which type of leprosy shows satellite lesions?_____

Borderline Tuberculoid (BT)

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