A patient has multiple recurrent ulcers of the tongue and buccal mucosa of several years' duration. A biopsy four years ago showed no malignancy, and neither nystatin nor chlorhexidine provides relief. What is the most appropriate next step to establish a diagnosis?

Correct answer: D. Incisional biopsy of perilesional tissue with direct immunofluorescence

• A. Blood work (CBC, ferritin, folate, B12, celiac serology, HbA1c) is a useful ADJUNCT for recurrent aphthous-like ulceration, but on its own it will not establish a mucosal diagnosis.
• B. Empiric antifungal therapy has already failed, and continuing it delays diagnosis of a potentially serious autoimmune condition.
• C. Cytology samples only surface cells; it cannot show the architectural or immunologic findings needed here and would miss all of the vesiculobullous diagnoses. It is a screening adjunct, not a diagnostic test for chronic ulceration.
• D. CORRECT (best clinical practice). Chronic recurrent oral ulceration unresponsive to antifungal and antiseptic therapy requires INCISIONAL BIOPSY of PERILESIONAL tissue, with a portion submitted in Michel's medium for DIRECT IMMUNOFLUORESCENCE. This is the only approach that can identify the immune-mediated vesiculobullous and lichenoid diseases in the differential — pemphigus vulgaris, mucous membrane pemphigoid, and erosive lichen planus — none of which can be diagnosed by cytology.

Note: Flag — source key disagrees with standard of care. The source keys EXFOLIATIVE CYTOLOGY. For chronic, recurrent, treatment-resistant oral ulceration the accepted approach is INCISIONAL BIOPSY WITH DIRECT IMMUNOFLUORESCENCE, because the differential (pemphigus, pemphigoid, erosive lichen planus) is defined immunohistologically. Discuss with the study group; if the exam offers immunofluorescence or incisional biopsy, choose that over cytology.