Widespread purplish-red plaques with plasma cell infiltrate: A rare type of lichen planus.

Diseases in which cutaneous plasma cell infiltrates predominate are rare and usually of unknown etiology, including those that transition from benign to malignant, such as cutaneous plasmacytosis, multicentric Castleman disease, and extramedullary plasmacytoma. These diseases may present as purplish, reddish-brown cutaneous plaques or nodules. Here, we report an exceptional case of lichen planus (LP) in which the patient had classic histopathological features, but the infiltrating inflammatory cells were plasma cells with restricted light chain expression. The patient presented with severe rashes, including purplish-red plaques and nodules, erythema, and erosions in the palmoplantar area, verrucous hyperplasia of the oral mucosa, and anonychia of the toes. These findings suggest a possible role of plasma cells with restricted light chain expression in the LP. Clinicians should closely follow patients for changes in their rash, perform repeat biopsies if necessary, and regularly conduct multisystemic evaluations.