Chromoblastomycosis — SCE Dermatology MCQ

Correct answer: D — Chromoblastomycosis

The correct answer is D, Chromoblastomycosis. The combination of a slowly progressive, well-defined verrucous plaque on an acral site (classically the foot, from traumatic inoculation of soil or plant matter) with pseudoepitheliomatous hyperplasia and, critically, intraepidermal microabscesses containing brown, thick-walled, septate muriform (sclerotic, Medlar) bodies is pathognomonic for chromoblastomycosis, a chronic fungal infection caused by dematiaceous moulds such as Fonsecaea pedrosoi. No other condition in the list produces muriform bodies; their presence on histology is diagnostic and distinguishes true fungal infection from reactive or neoplastic verrucous lesions. The chronicity (years) and indolent, expanding course also fit a slow-growing implantation mycosis rather than an acute or rapidly evolving process. Why the other options are wrong: B. Keratoacanthoma: This is a rapidly growing (weeks), crateriform squamoproliferative lesion that typically involutes spontaneously; it shows keratin-filled crater on histology, not fungal muriform bodies. E. Squamous cell carcinoma: SCC shows atypical keratinocytes with invasive nests and variable differentiation, but no yeast forms or sclerotic bodies; pseudoepitheliomatous hyperplasia can mimic SCC clinically and histologically, which is a recognised diagnostic pitfall in chromoblastomycosis. A. Tuberculosis verrucosa cutis: This shows granulomatous inflammation with caseating necrosis and acid-fast bacilli on special stains, not pigmented fungal elements. C. Verruca vulgaris: Viral wart histology shows koilocytes, hypergranulosis and papillomatosis from HPV infection, with no fungal microabscesses. Key point: Muriform (sclerotic, Medlar) bodies on histology are pathognomonic for chromoblastomycosis and immediately exclude the mimics of verrucous plaques listed.

Reference: DermNet chromoblastomycosis review: https://dermnetnz.org/topics/chromoblastomycosis