Micro & Immunology · patient case question
Four weeks later he returns with symmetric target-shaped lesions with concentric rings on his forearms, along with crusted, bleeding lips. What immunologic mechanism underlies this presentation?
Patient case: Rash After Local Anesthetic in a Child
Patient: 10-year-old male
Chief Complaint: Restorative treatment on two mandibular molars.
Background: Healthy, no known allergies, no previous dental treatment requiring anesthesia. Immunizations current.
Medications: None
Vital Signs: Baseline: BP 100/62 mmHg · HR 86 bpm · RR 18 · T 98.4°F
Findings: Twenty minutes after administration of 2% lidocaine with 1:100,000 epinephrine, he develops a generalized raised urticarial rash over the trunk and arms, accompanied by nausea, one episode of vomiting, and loose stools. Mild expiratory wheeze is audible. Airway is patent, phonation is normal, and blood pressure remains stable at 98/60 mmHg.
Show answer and explanation
Correct answer: B. Type IV — delayed, cell-mediated
- A. Incorrect. Immune complex deposition causes vasculitis, palpable purpura, arthralgia, and nephritis — a different clinical picture.
- B. Correct. This is a T cell-mediated process. Cytotoxic CD8 lymphocytes attack keratinocytes displaying a drug or infectious antigen, producing the characteristic epidermal necrosis. The delayed onset weeks after exposure is itself the clue to a cell-mediated mechanism.
- C. Incorrect. Type II reactions target cell surface antigens on circulating or fixed cells, causing lysis. They do not produce target lesions on skin.
- D. Incorrect. A type I reaction would have occurred within minutes to hours of exposure, as his first reaction did. Four weeks is far too long an interval.
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