Amelanotic Melanoma — SCE Dermatology MCQ

Correct answer: E — Amelanotic melanoma

The correct answer is E, amelanotic melanoma. A rapidly growing, non-pigmented (amelanotic) papule or nodule with polymorphous vessels (a mixture of dotted, linear irregular, and hairpin patterns) on dermoscopy is the classic and most dangerous mimic pattern for melanoma lacking melanin. Because pigment network, blotches, and other melanin-specific clues are absent, amelanotic melanoma is frequently misdiagnosed clinically as a benign vascular or cystic lesion, which delays diagnosis and worsens prognosis. Any solitary lesion with this vascular polymorphism and a short growth history must be regarded as melanoma until proven otherwise and referred urgently for excision biopsy and histology. Why the other options are wrong: C. Glomus tumour: typically presents as a tender, blue-red subungual or acral nodule with severe pain on minimal pressure or cold exposure, not an ear nodule with polymorphous vessel dermoscopy. D. Cherry angioma: shows dermoscopically as uniform red-purple lacunae with a homogeneous vascular pattern, not the irregular polymorphous mixture (dotted, linear, hairpin) seen here, and it grows slowly rather than over three weeks. B. Sebaceous cyst: presents as a skin-coloured, fluctuant, non-vascular swelling often with a central punctum; dermoscopy does not show polymorphous vessels since there is no vascular proliferation. A. Pyogenic granuloma: also vascular and rapidly growing, but characteristically shows a homogeneous reddish colour with white collarette and regular vascular structures, lacking the polymorphous, irregular mixture that raises concern for malignancy. Key point: a rapidly enlarging, amelanotic nodule showing polymorphous (mixed dotted, linear irregular, hairpin) vessels on dermoscopy must be treated as amelanotic melanoma until excision biopsy proves otherwise, since absence of pigment does not exclude melanoma and delays diagnosis.

Reference: British Journal of Dermatology (Oxford Academic), 'Teledermoscopy: a helpful detection tool for amelanotic and hypomelanotic melanoma', 2021: dermoscopic features of amelanotic/hypomelanotic melanoma include polymorphous vessels (dotted, linear, coiled), milky-red areas, short white lines and grey dots/granules. https://academic.oup.com/bjd/article-abstract/185/6/1244/6599886