Papulonodular Lesions with Scale and/or Crust

Abstract

The differential diagnosis includes pityriasis lichenoides et varioliform acuta (PLEVA), lymphomatoid papulosis (LyP), secondary syphilis, nodular scabies, prurigo nodularis (PN), nodular pemphigoid (NP), and disseminated infection. Histology is very helpful.

A mature lesion of PLEVA shows diffuse parakeratosis, loss of the granular layer, regular acanthosis, moderate dyskeratosis, basal vacuolization, and a purely lymphocytic infiltrate in the superficial, and to a lesser degree, the deep dermis. Extravasated red cells may be seen.

The histological findings in LyP are variable. PN, NP, nodular scabies and nodular syphilis all share significant epidermal hyperplasia but differ in many regards that makes differentiation among them rather easy. Scabies organisms may rarely be found in the horny layer in a lesion of nodular scabies. The characteristic dermal findings are those of a “persistent hypersensitivity reaction” or “pseudolymphoma.”