Micro & Immunology · patient case question
Which type of hypersensitivity reaction does this represent?
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: C. Type I — immediate, IgE-mediated
- A. Incorrect. Type IV reactions are T cell-mediated and take 24 to 72 hours to develop. Contact dermatitis to latex or nickel is the classic dental example.
- B. Incorrect. Type II reactions involve IgG or IgM directed against cell surface antigens, producing complement-mediated cell lysis. Examples include hemolytic transfusion reactions and Goodpasture syndrome. They do not present acutely as urticaria.
- C. Correct. Onset within minutes, urticaria, gastrointestinal symptoms, and bronchospasm together define an immediate IgE-mediated reaction. Antigen cross-links IgE bound to mast cells and basophils, which degranulate and release histamine, tryptase, and leukotrienes.
- D. Incorrect. Type III reactions involve circulating antigen-antibody complexes depositing in tissue, causing vasculitis, serum sickness, or glomerulonephritis. Onset takes days rather than minutes.
Note: Worth knowing: true allergy to an amide anesthetic is rare. Reactions are far more often attributable to the methylparaben preservative, to sodium metabisulfite in epinephrine-containing solutions, to latex, or to intravascular injection producing a systemic response mistaken for allergy.
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