Rash After Local Anesthetic in a Child

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.

Correct answer: A. Urticarial rash

• A. Correct. Urticaria — raised, pruritic, blanching wheals — is the direct visible consequence of mast cell histamine release increasing vascular permeability. It is the most specific of the findings listed for an allergic mechanism.
• B. Incorrect. Nausea is entirely non-specific. It accompanies vasovagal syncope, anxiety, and many drug effects with no immune basis at all.
• C. Incorrect. Diarrhea is part of the gastrointestinal component of anaphylaxis, but taken alone it does not distinguish an allergic reaction from gastroenteritis or an anxiety response.
• D. Incorrect. Vomiting occurs in an allergic reaction but occurs just as readily with anxiety, pain, and vasovagal episodes.

Correct answer: A. Administer a systemic antihistamine such as diphenhydramine

• A. Correct. For a reaction limited to skin and mild gastrointestinal symptoms with a stable airway and stable hemodynamics, an H1 antihistamine is appropriate. Discontinue the suspected agent, monitor closely, and arrange medical evaluation with allergy referral for definitive identification of the trigger.
• B. Incorrect. Intramuscular epinephrine is the immediate treatment for anaphylaxis — airway compromise, stridor, significant bronchospasm, or hypotension. His airway is patent and pressure is stable. That said, if his condition deteriorates at any point, epinephrine must be given without hesitation and takes absolute priority.
• C. Incorrect. Observation alone is inadequate when a systemic reaction with cutaneous, gastrointestinal, and respiratory features is already established.
• D. Incorrect. A topical agent cannot treat a systemic reaction involving multiple organ systems.

Note: Do not become complacent because vitals are currently stable. Biphasic anaphylaxis can recur hours after apparent resolution, which is why medical evaluation and a period of observation are part of the plan.

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.

Correct answer: B. Erythema multiforme

• A. Incorrect. Erosive lichen planus presents with bilateral reticular white striae and erosions, follows a chronic waxing and waning course, and does not cause target lesions on the skin.
• B. Correct. Symmetric target or iris lesions on the extremities with hemorrhagic, crusted lips are the defining presentation of erythema multiforme. It is most often triggered by herpes simplex virus or by medications, and it characteristically affects young patients with abrupt onset.
• C. Incorrect. Primary herpetic gingivostomatitis affects young children with fever, malaise, and fiery erythematous gingivitis with vesicles throughout the mouth. Skin target lesions are not part of it.
• D. Incorrect. Pemphigus vulgaris produces flaccid intraoral bullae with a positive Nikolsky sign, affects patients typically in their fifth and sixth decades, and does not produce target lesions.

Note: Recognize the spectrum: erythema multiforme minor involves one mucosal site with limited skin lesions. Stevens-Johnson syndrome and toxic epidermal necrolysis represent the severe end, defined by the percentage of body surface area detached, and both are medical emergencies.

Correct answer: A. Systemic corticosteroids with supportive care and withdrawal of the trigger

• A. Correct. Management centers on identifying and removing the trigger, systemic corticosteroids for significant cases, and supportive care — hydration, analgesia, topical anesthetic rinses, and a soft diet. Where herpes simplex is the recurrent precipitant, prophylactic antiviral therapy prevents further episodes.
• B. Incorrect. Debridement would worsen an already compromised epithelial surface and has no place in management.
• C. Incorrect. This is an immune-mediated process, not a fungal infection. Antifungals have no role.
• D. Incorrect. Antibiotics are not indicated and are frequently the trigger. Sulfonamides, penicillins, and anticonvulsants are among the commonest drug causes.