FIGURE 88.7 Spitz nevus Yellow, Tan, or Brown Papules Many papules are yellow, tan, or brown These include the lesions seen in urticaria pigmentosa (see Chapter 69 Rash: Neonatal ), flat warts, xanthomas, insect bites, juvenile xanthogranulomas (JXGs) as well as melanocytic nevi One way to differentiate the various papules from one another is to scratch them If hiving of a scratched lesion (Darier sign) occurs within a short period of time (3 to minutes), the lesion likely contains mast cells (i.e., a mastocytoma or urticaria pigmentosa) ( Fig 88.9 ) Make sure to scratch normal skin to rule out the presence of dermatographism The latter condition will produce a falsepositive Darier sign When no urtication occurs, a biopsy may be helpful Flat warts tend to be grouped, are flat topped, and can be autoinoculated in scratch lines (pseudo-Koebner phenomenon) Lesions characteristic for JXGs are not flat topped, tend to be singular in number (or when multiple are scattered about), and not demonstrate the Koebner phenomenon (recapitulation of the eruption in