Plasma Cell-Predominant Lichen Planopilaris

Lichen planopilaris (LPP) is a scarring alopecia that is characterized by a lichenoid interface infiltrate with follicular extension. We present a case of LPP composed predominantly of plasma cells in a 52-year-old man. The patient was originally diagnosed with scalp psoriasis 30 years before presentation. Punch biopsies performed at an outside institution 2 years before presentation revealed lymphocyte-predominant LPP. After referral to the senior author's institution due to inadequate response to therapy, biopsies demonstrated a robust, superficial, and deep lichenoid interface dermatitis composed predominantly of plasma cells. Immunohistochemical and special staining for CD138, MUM-1, kappa and lambda light chains, immunoglobulin G4, CD3, CD20, PAX5, CD5, CD7, CD4, CD8, CD43, CD123, Gram, Grocott's methenamine silver stain, treponemal antibody, colloidal iron, and Movat showed a scarring alopecia and were not supportive of a hematolymphoid, infectious, or autoimmune etiology. B-cell clonality studies were below the threshold needed for definitive diagnosis of a clonal process. Doxycycline and hydroxychloroquine were subsequently added to the patient's treatment regimen, leading to an improvement of symptoms. We present this case to bring awareness to this unusual feature and discuss its differential diagnosis.