Acral Dermoscopy — SCE Dermatology MCQ

Correct answer: E — Benign acral melanocytic lesion (parallel furrow pattern is the most common benign acral dermoscopic pattern)

The correct answer is E, benign acral melanocytic lesion, because the parallel furrow pattern is the classic and most common benign dermoscopic pattern seen on palmar and plantar skin. In this pattern, pigment tracks along the furrows (sulci) of the dermatoglyphics rather than the ridges, reflecting melanocytic nests confined to the crista profunda limitans beneath the sulcus. This contrasts with the parallel ridge pattern, in which pigment sits on the ridges and is the classic sign of acral lentiginous melanoma. Given a 50-year-old man with a solitary palmar macule and a furrow-based pattern, and no atypical features described, this is best explained as a benign acral naevus rather than melanoma, so routine reassurance with safety-netting (or excision only if other suspicious features develop) is appropriate rather than urgent biopsy. Why the other options are wrong: C. Tinea nigra: this fungal infection produces a diffuse brown-black stain with fine pigmented streaks that do not respect the furrow-ridge architecture, and there is no follicular or dermatoglyphic-aligned parallel pattern; it also lacks the structured pigment network seen here. B. Melanoma: acral melanoma is signalled dermoscopically by the parallel ridge pattern (pigment on the ridges, often with a broadened, irregular band and overlying white dots), not the furrow pattern described in this stem. A. Haematoma: subcorneal haematoma shows red-black to purple-black homogeneous colour, often with peripheral fading, small satellite globules and a lack of a true pigment network confined to furrows; it does not create a structured parallel furrow pattern of melanin. D. Wart: viral warts show interrupted skin lines with papillomatous surface change and often visible looped or dotted vessels on dermoscopy, not a parallel pigmented furrow pattern. Key point: pigment localised to the furrows (parallel furrow pattern) indicates a benign acral naevus, whereas pigment on the ridges (parallel ridge pattern) is the discriminating sign of acral melanoma.

Reference: DermNet NZ, Acral lentiginous melanoma dermoscopy (reviewed, widely used UK clinical reference): https://dermnetnz.org/topics/acral-lentiginous-melanoma-dermoscopy