Pseudo-Hutchinson’s sign – Unraveled by dermoscopy
A 13-year-old boy presented with a history of asymptomatic black band on the nail of the right little finger of 1 year duration. On examination, he manifested a brown-black linear band of 2 mm width with regular borders and striate leukonychia on the right little finger [Figure 1]. Black pigmentation extending to proximal nail fold was observed. Dermoscopy revealed a regular patterned brown-black band of 2 mm width with homogeneity of color and width of each individual line [Figure 2]. The black pigmentation extending to proximal nail fold was found to be the nail plate pigmentation visible through a translucent cuticle, known as pseudo- Hutchinson’s sign [Figure 3]. A diagnosis of longitudinal melanonychia secondary to benign melanocytic proliferation was made (nevus/lentigo).
Pseudo-Hutchison’s sign is a reflection of the pigmentation of nail bed and nail matrix through the transparent nail folds, whereas Hutchinson’s sign is a feature of subungual melanoma where brown-black pigmentation from longitudinal melanonychia extends onto the proximal and lateral nail folds.
Melanonychia assumes significance since it can be a manifestation of nail apparatus melanoma. Apart from Hutchinson’s sign, other warning signs that should raise suspicion of melanoma manifesting as melanonychia include onset during fourth decade of life or later, personal or family history of melanoma or dysplastic nevus syndrome in the affected, dystrophy of the affected nail, width of pigmentation >3 mm, blurred and indistinct margins or variations in band color, and widening or darkening of pigmentation proximally.