Lichenoid dermatitis in paraneoplastic pemphigus: a pathogenic trigger of epitope spreading?

BACKGROUND: In select cases, lichen planus has been observed to be a paraneoplastic condition sometimes associated with paraneoplastic pemphigus, a disease featuring autoantibodies directed against plakin proteins, desmogleins 3 and 1, and a still uncharacterized 170-kd antigen. Epitope spreading describes the phenomenon where underlying chronic inflammation leads to the sequential recognition of new epitopes on self-proteins over time. OBSERVATIONS: Five of 6 patients diagnosed as having paraneoplastic pemphigus had concomitant clinical and histological features of lichen planus. In 1 patient, results of the initial indirect immunofluorescence on rat bladder were negative and only 2 of the 5 antigens were identified by immunoprecipitation. After 1 year of worsening disease, repeated testing confirmed the presence of antibodies directed against all 6 of the implicated antigens, supportive of our hypothesis that epitope spreading may occur in paraneoplastic pemphigus. CONCLUSIONS: Lichenoid eruptions may predispose to an early evolutionary stage of paraneoplastic pemphigus. Cell-mediated autoimmunity at the dermoepidermal junction may promote the exposure of self-antigens and the development of subsequent and progressive humoral autoimmunity. As such, paraneoplastic pemphigus may demonstrate epitope spreading in a human, humoral-mediated autoimmune disease.