Bowen disease — SCE Dermatology MCQ

Correct answer: E — Skin biopsy to confirm intraepidermal carcinoma

The correct answer is E, skin biopsy to confirm intraepidermal carcinoma. A slowly enlarging, well-demarcated erythematous scaly plaque on the lower leg in an older woman that has failed both topical corticosteroid and antifungal treatment for over a year is the classic presentation of Bowen disease (squamous cell carcinoma in situ), which is frequently misdiagnosed as eczema, psoriasis or tinea. Because the lesion mimics benign inflammatory and fungal conditions but persists despite appropriate empirical therapy, histological confirmation is required both to establish the diagnosis and, critically, to exclude early invasive transformation into frank SCC. PCDS and BAD guidance state that biopsy is indicated whenever there is diagnostic uncertainty, and any feature suggesting invasion mandates urgent pathway referral rather than further empirical treatment. Why the other options are wrong: C. Repeat fungal culture after another steroid course: a prior negative response to antifungal treatment already argues against dermatophyte infection, and further steroid use would blur histology and delay cancer diagnosis. D. Serum antinuclear antibody testing: ANA is used to investigate connective tissue disease such as lupus, which does not present as a solitary, treatment-resistant scaly plaque of this duration. B. Patch testing to leg-ulcer dressings: there is no ulcer or dressing exposure described, and patch testing addresses contact allergic dermatitis, not a scaly malignant plaque. A. Wood lamp examination for erythrasma: erythrasma shows coral-pink fluorescence but presents as flexural, ill-defined patches, not a well-demarcated, treatment-refractory scaly plaque, and it would not explain 14 months of progression. Key point: a persistent, treatment-resistant scaly erythematous plaque in an older adult always requires biopsy to exclude Bowen disease or invasive SCC before further empirical topical therapy.

Reference: British Association of Dermatologists, guidelines for the management of people with cutaneous squamous cell carcinoma in situ (Bowen disease), British Journal of Dermatology 2022; https://academic.oup.com/bjd/article/188/2/186/6788751