Diagnostic approach in lymphoplasmacytic plaque

BACKGROUND: Lymphoplasmacytic plaque (LPP) is a recently described rare skin disease characterized by a dense dermal lymphohistiocytic infiltrate with polyclonal plasma cells. The clinical picture is distinct with reddish to brownish plaque with a predilection for the lower leg. LPP typically affects children. OBJECTIVE: To define clinical and histologic criteria of LPP and to develop a diagnostic flow chart. METHODS: We investigated six of our own LPP cases. Immunoglobulin light chains, IgG, IgG4, CD31, CD163 as a histiocytic marker were examined by immunohistochemistry. PCR-based molecular studies were conducted for borrelia sp., mycobacterial and leishmania sp. Moreover, 10 cases, which have been reported in the literature, were checked for the same features. RESULTS: We could differentiate three main histological patterns (superficial band-like only, [deep] dermal only and mixed). Acanthosis and interface dermatitis are key features in cases with a superficial band-like or mixed infiltrate. Granulomas and giant cells could be only found in about 30% of the cases. The number of plasma cells was variable accounting for 5-40% of the infiltrate. The number of blood vessels was increased in the majority of the cases. 'Free-floating' collagen bundles surrounded by histiocytes (pseudorosettes) were identified as a new histological feature. An infectious agent could be excluded in all cases. CONCLUSIONS: LPP is a long-standing skin disease, which may also occur in adults and in other body regions than the lower leg. Reproducible clinical and histological criteria allow delineating a diagnostic work-up for LPP.