A borderline lepromatous patient on multidrug therapy develops crops of painful erythematous nodules over the trunk and limbs with fever and arthralgia. Biopsy of a nodule shows a dense neutrophilic infiltrate around dermal vessels. The immunopathological basis of this reaction is:
- A Immune complex deposition with complement activation (type III hypersensitivity) ✓
- B Type IV delayed hypersensitivity to M. leprae antigens
- C Direct toxic effect of dapsone on dermal vessels
- D Autoimmune destruction of Schwann cells by cytotoxic T cells
Correct answer: A. Immune complex deposition with complement activation (type III hypersensitivity)
Explanation
Erythema nodosum leprosum, the Type 2 lepra reaction, results from circulating immune complexes of M. leprae antigen and antibody depositing in vessels, activating complement and attracting neutrophils, producing a small vessel vasculitis. Type 1 reversal reactions, by contrast, are cell-mediated delayed hypersensitivity events with lymphocytic infiltration and oedema, and they occur without systemic vasculitic features.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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