Leprosy reaction Type 1 (reversal reaction) must be distinguished from Type 2 (erythema nodosum leprosum, ENL). Which feature is characteristic of Type 1 reversal reaction?
- A Tender erythematous subcutaneous nodules on the limbs and face
- B Upgrading of immune response with oedematous, erythematous pre-existing skin lesions and acute nerve function impairment ✓
- C Systemic features including fever, uveitis, arthritis, and orchitis
- D Occurs exclusively in tuberculoid leprosy patients
Explanation
Type 1 (reversal) reaction is a delayed-type (Type IV) hypersensitivity upgrade in immune response occurring in borderline leprosy (BT, BB, BL). It presents as sudden oedema and erythema of pre-existing skin lesions with acute nerve function impairment (NFI) — the major cause of irreversible disability if not promptly treated with steroids. ENL (Type 2) is an immune-complex (Type III) mediated reaction with tender erythematous nodules, systemic fever, uveitis, and orchitis, occurring in lepromatous/borderline-lepromatous disease. Type 1 is NOT exclusive to tuberculoid disease.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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