Children with the above presentation are more likely to have PLEVA, bites, or scabies. NP favors the elderly. Disseminated infection often occurs in immunosuppressed individuals.

Lesions that vary in morphology with time and some of which heal with scar strongly favor PLEVA and LyP (classic type), while lesions that are pruritic and appear lichenified are likely PN more often than nodular scabies and NP. Genital lesions favor scabies; mucosal lesions favor secondary syphilis .

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There is almost no overlap among the histological features between the above seven disorders.

A mature lesion of PLEVA that is a red papule with a surface change of both scale and mild crust before the phase of the erosion, and after the phase of smooth, red papule shows such characteristic changes that the diagnosis may be made with absolute certainty. The findings include diffuse parakeratosis, loss of the granular layer replaced by pale superficial epidermis, regular acanthosis, moderate dyskeratosis, basal vacuolization, and a generally moderate, purely lymphocytic infiltrate in the superficial and (to a lesser degree) the deep dermis. The monomorphous nature of the infiltrate is quite characteristic. The presence of other cell types denies the diagnosis of PLEVA. Extravasated red cells may be seen both in the papillary dermis as well as in the epidermis.