A 48-year-old man has a longitudinal dark band on his right thumbnail that has widened over 8 months. The pigmentation extends onto the proximal nail fold and adjacent skin, and the band is broadest at its proximal end. The next best step is:

• A Reassure and review in one year
• B Biopsy of the nail matrix ✓
• C Topical corticosteroid under occlusion
• D Oral antifungal therapy for 3 months

Explanation

Longitudinal melanonychia that widens proximally over months, becomes broader than 3 mm, and shows Hutchinson sign, extension of pigment to the proximal nail fold and hyponychium, indicates subungual melanoma arising from the nail matrix. Biopsy of the matrix is mandatory for diagnosis. Benign melanonychia is stable and narrow, and Hutchinson sign is absent. Antifungals treat onychomycosis, which can mimic pigmentation but lacks the Hutchinson sign.

Reference: Rook's Textbook of Dermatology, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.