Subcorneal Pustular Dermatosis — SCE Dermatology MCQ

Correct answer: B — Dapsone

The correct answer is B, Dapsone. Sneddon-Wilkinson disease (subcorneal pustular dermatosis) is a rare relapsing neutrophilic dermatosis, and dapsone represents the first-line therapy, with lesions typically resolving over about a month and low-dose maintenance often needed to prevent relapse. Its mechanism relates to neutrophil-suppressing anti-inflammatory effects (inhibition of neutrophil chemotaxis and myeloperoxidase activity), which targets the neutrophilic infiltrate seen histologically without invoking broad immunosuppression. The subcorneal pustules without acantholysis and negative direct immunofluorescence exclude pemphigus foliaceus and IgA pemphigus, disorders that would otherwise mimic this presentation but are not dapsone's classic indication in the same way. G6PD status should be checked before starting, as dapsone causes dose-dependent haemolysis. Why the other options are wrong: C. Oral Prednisolone: Systemic corticosteroids are used as a second-line or adjunct option for resistant or extensive disease, not first-line, and long-term use carries significant adverse effect burden without the established efficacy profile of dapsone in this condition. A. Rituximab: This is reserved for refractory, treatment-resistant cases unresponsive to dapsone and other conventional agents; it is not appropriate as initial therapy given cost, immunosuppression risk, and lack of first-line evidence. D. Oral Methotrexate: Methotrexate is an alternative or adjunctive agent used in cases where dapsone is ineffective or contraindicated, but it lacks the rapid, reliable response and established first-line status of dapsone in Sneddon-Wilkinson disease. E. Topical corticosteroids alone: Topical steroids may provide symptomatic relief but do not adequately control the neutrophilic pustular eruption or address the systemic disease process, so they are insufficient as monotherapy. Key point: Dapsone is the first-line treatment of choice for Sneddon-Wilkinson disease, with G6PD screening required before initiation.

Reference: DermNet NZ, Subcorneal pustular dermatosis, 2024, https://dermnetnz.org/topics/subcorneal-pustular-dermatosis