A 64-year-old woman with MRSA endocarditis develops a tense bullous eruption on day 8 of intravenous vancomycin therapy. Examination reveals tense, fluid-filled bullae arranged in characteristic annular and polycyclic plaques with new lesions forming at the periphery of older lesions — producing a "string of pearls" appearance. Lesions favor the trunk, buttocks, and groin, with mucosal involvement of the oral cavity. Punch biopsy shows a subepidermal blister with neutrophil-predominant infiltrate. Direct immunofluorescence of perilesional skin is shown in the diagram at **B**. Which of the following is the most appropriate next step in management?

Question

Accepted Answer

A. Discontinue vancomycin immediately and initiate dapsone after G6PD screening. ## Why "Discontinue vancomycin immediately and initiate dapsone after G6PD screening" is right

The structure marked **B** shows linear IgA deposition along the basement membrane zone in a characteristic "string of pearls" pattern — pathognomonic for Linear IgA Bullous Disease (LABD). In the adult setting, vancomycin is the most common and best-characterized drug trigger for LABD. The clinical presentation (tense bullae, annular/polycyclic arrangement, mucosal involvement, neutrophil-predominant subepidermal blister, and linear IgA on DIF) confirms drug-induced LABD. Management mandates immediate withdrawal of the offending agent; drug-induced disease typically resolves 2–6 weeks after discontinuation. First-line systemic therapy is dapsone (after mandatory G6PD screening to exclude deficiency and risk of hemolysis), which controls disease in days. [British Association of Dermatologists Autoimmune Bullous Disease Guidelines; Bolognia 5e]

## Why each distractor is wrong

- **Continue vancomycin with topical corticosteroids only**: Continuing the offending drug perpetuates the autoimmune response and prevents resolution. Topical therapy alone is insufficient for extensive mucosal and cutaneous disease. The anchor diagnosis requires drug withdrawal.
- **Switch to cephalosporin-based antibiotic therapy with systemic corticosteroids**: Although cephalosporins are an alternative for MRSA coverage, ceftriaxone itself is a known trigger of LABD in some cases. Systemic corticosteroids are not first-line for LABD; dapsone is superior and acts more rapidly.
- **Perform HLA-DQ2/DQ8 testing and initiate a gluten-free diet**: This approach is appropriate for dermatitis herpetiformis (DH), which presents with granular IgA in dermal papillae and is associated with celiac disease. The linear IgA along the BMZ at **B** excludes DH and confirms LABD, which is not gluten-related.

**High-Yield:** Vancomycin-induced LABD in adults: withdraw drug + dapsone (after G6PD screen) = rapid resolution; linear IgA at BMZ distinguishes LABD from granular IgA in dermal papillae of DH.

[British Association of Dermatologists Autoimmune Bullous Disease Guidelines; Bolognia 5e]

Answer

B. Continue vancomycin with topical corticosteroids only

Answer

C. Switch to cephalosporin-based antibiotic therapy with systemic corticosteroids

Answer

D. Perform HLA-DQ2/DQ8 testing and initiate a gluten-free diet

Explanation

Why "Discontinue vancomycin immediately and initiate dapsone after G6PD screening" is right

Why each distractor is wrong

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