Leprosy

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.

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).

⭐ 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.

⭐ 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.

Management & Reactions - Healing & Hazards

• MDT Regimens (WHO):

  Category	Drugs	Duration
  PB	Rifa (600mg M) + Dap (100mg D)	6 mo
  MB	Rifa (600mg M) + Dap (100mg D) + Clofa (300mg M, 50mg D)	12 mo
  SLPB	SDR: 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.