Two leprosy patients develop acute neuritis during treatment. Patient 1, borderline tuberculoid disease, has new erythematous swelling of existing plaques with severe ulnar nerve tenderness within 6 months of starting therapy. Patient 2, lepromatous disease, has fever and tender nodules. The immune mechanisms underlying these two reactions respectively are:

• A Both are antibody mediated complement activation reactions
• B Type III immune complex deposition and type IV delayed hypersensitivity
• C Both are type IV delayed hypersensitivity reactions
• D Type IV delayed hypersensitivity and type III immune complex deposition ✓

Explanation

Reversal (type 1) reaction is a delayed type IV hypersensitivity response against M. leprae antigens, seen in borderline disease, marked by inflammation of pre-existing lesions and nerve damage, and treated with corticosteroids. Erythema nodosum leprosum (type 2) is a type III immune complex reaction with systemic features and neutrophilic panniculitis, treated with thalidomide or steroids. Confusing the two mechanisms is the classic error.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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