A pretibial plaque in a five and a half year-old girl

A five and a half year-old girl presented with a reddish-brown plaque on her right anterior tibia, first observed 1 year previously and without any history of injury or insect bite. Histological examination showed a dense dermal infiltrate composed of plasma cells and small lymphocytes, combined with lymphocytic exocytosis in the epidermis and interface dermatitis. In addition, a second biopsy found small epithelioid granulomas within the lymphoplasmocytic infiltrate. Infection was ruled out. No clonality was found. None of the treatments attempted was successful (antibiotics and steroids), and the lesion was stable but did not improve for 4 years. The same features typical of lymphoplasmocytic pseudolymphoma were observed on a third biopsy. A diagnosis of "pretibial lymphoplasmocytic plaque" was made on the basis of clinical and histological findings. Recently, 3 other cases of this type of lymphocytic and plasma cell cutaneous infiltrate with very distinctive clinical and histopathological features have been reported in children. Our case is instructive because it presents new and as yet undocumented histopathologic features including a lichenoid reaction with vacuolization of the basal cell layer and numerous apoptotic bodies, apparent in 2 of the 3 biopsies, and hypervascularity with thick-walled blood vessels lined with plump endothelial cells in the upper dermis. The clinicopathological presentation of these cases, including ours, is homogenous suggesting a specific entity described as "pretibial lymphoplasmocytic plaque in children". This seems to be a benign, chronic, reactive process, probably arising secondary to a local response to an unknown antigen.