A farmer develops intense swelling and tenderness at the site of a previous tuberculin test within 4 to 8 hours of a repeat intradermal injection. Histology shows neutrophil-rich vasculitis with fibrinoid necrosis of small vessels. This localized reaction results from immune complex deposition after antigen enters a previously sensitized host and is known as the:
- A Koebner phenomenon
- B Schwartzman reaction
- C Arthus reaction ✓
- D Jarisch-Herxheimer reaction
Correct answer: C. Arthus reaction
Explanation
The Arthus reaction is a localized type III (immune complex) reaction occurring when antigen is injected into a previously sensitized individual; circulating IgG complexes form locally, activate complement, and recruit neutrophils causing edema and necrotizing vasculitis within hours. The Schwartzman reaction is cytokine-mediated and biphasic without antibodies, Koebner describes lesion induction by trauma in psoriasis, and Jarisch-Herxheimer follows antibiotic killing of spirochetes.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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