Track: Case Reports

Abstract:

Introduction: Lymphoplasmacytic plaque (LPP) is an uncommon benign skin condition characterized by a dense lymphohistiocytic dermal infiltrate with admixed polyclonal plasma cells. Initially described in children as a solitary asymptomatic, reddish-brown plaque on the pretibial area, more recent reports have identified adult-onset cases involving atypical anatomical sites. We present an unusual case of LPP in an adult female on the upper extremity.

Case Presentation: A 46-year-old Japanese female presented with a 5-month history of a persistent pink plaque on the right upper arm. She denied preceding trauma, insect bites, or other precipitating factors. Physical examination revealed a well-circumscribed 18x20mm erythematous thin plaque with mild infiltrate and central atrophy on the right upper arm. Histopathological evaluation showed an acanthotic epidermis with a dense nodular and diffuse inflammatory infiltrate of lymphocytes, histiocytes, plasma cells, and focal clusters of multinucleated giant cells in the superficial dermis focally extending to the deep dermis. Microbial stains were negative and in-situ hybridization for kappa and lambda light chains revealed no restriction. The lesion was treated with intralesional steroids.

Discussion: LPP is an emerging clinicopathologic entity with an expanding demographic and anatomical distribution. Diagnosis requires correlating histological features of a dermal lymphohistiocytic infiltrate with polyclonal plasma cells with the clinical findings of a solitary reddish-brown plaque without evidence of systemic involvement. Adult-onset LPP must be differentiated from cutaneous plasmacytosis, which is typically multifocal and associated with systemic involvement. While surgical excision remains the definitive treatment, treatment with intralesional steroids and pulsed dye laser have shown benefit.