Which biopsy technique is indicated to diagnose a vesiculobullous immune-mediated mucosal disease?

Correct answer: C. Perilesional incisional biopsy for direct immunofluorescence

• A. Incorrect. These lesions are diffuse and multifocal; excision is neither possible nor diagnostic.
• B. Incorrect. Brush biopsy samples surface cells only and cannot demonstrate the subepithelial or intraepithelial split and immune deposits.
• C. Correct. Tissue must be taken from clinically NORMAL mucosa adjacent to the lesion, because the immune deposits (IgG, C3) are destroyed within the ulcer bed itself. The perilesional specimen goes into Michel's medium for direct immunofluorescence.
• D. Incorrect. Culture identifies microorganisms and is irrelevant to an autoimmune process.