Herald patch preceding a diffuse eruption in a Christmas-tree pattern along skin lines is characteristic of which condition?

Herald patch preceding a diffuse eruption in a Christmas-tree pattern along skin lines is characteristic of which condition?

• A. Psoriasis
• B. Pityriasis rosea
• C. Lichen planus
• D. Seborrheic dermatitis

Answer: (B)

This presentation is classic for pityriasis rosea. It starts with a herald patch, a single oval lesion that may be followed days to weeks later by a diffuse eruption on the trunk. The new lesions tend to align along the skin’s cleavage lines (Langer’s lines), creating a Christmas-tree pattern, especially on the back. The condition is usually seen in adolescents and young adults and is self-limited over several weeks to months. Other conditions don’t follow this sequence with the same pattern: psoriasis typically shows well-demarcated plaques with silvery scales on extensor surfaces; lichen planus presents as pruritic, purple, polygonal papules with Wickham’s striae; seborrheic dermatitis features greasy scales and erythematous patches in seborrheic areas, not the herald patch followed by a trunk-wide tree-like distribution.

This presentation is classic for pityriasis rosea. It starts with a herald patch, a single oval lesion that may be followed days to weeks later by a diffuse eruption on the trunk. The new lesions tend to align along the skin’s cleavage lines (Langer’s lines), creating a Christmas-tree pattern, especially on the back. The condition is usually seen in adolescents and young adults and is self-limited over several weeks to months.

Other conditions don’t follow this sequence with the same pattern: psoriasis typically shows well-demarcated plaques with silvery scales on extensor surfaces; lichen planus presents as pruritic, purple, polygonal papules with Wickham’s striae; seborrheic dermatitis features greasy scales and erythematous patches in seborrheic areas, not the herald patch followed by a trunk-wide tree-like distribution.