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In this study, four patients without detectable autoantibodies and without evidence of acantholysis were diagnosed with paraneoplastic pemphigus as defined by (1) extensive, refractory mucous-membrane ulcerations involving the lips, oral mucosa, eyes, and esophagus; (2) known or occult malignancy (such as non-Hodgkin lymphoma, Castleman disease, thymoma, Waldenström macroglobulinemia, and spindle cell sarcoma); and (3) histologic demonstration of a brisk lichenoid interface dermatitis.
No patients showed acantholysis of the affected skin, and none had IgG bound in the intercellular areas of the epidermis. Testing by both indirect immunofluorescence and immunoprecipitation techniques failed to find circulating antibodies to epidermal antigens, including the desmosomal and plakin antigens implicated in the pathogenesis of paraneoplastic pemphigus. All four patients had received rituximab prior to the study, presumably as treatment for their underlying lymphomatous neoplasms. The authors propose that a variant of paraneoplastic pemphigus can present with the typical lichenoid features but without the typical acantholytic features and autoantibodies. They suggest that CD8+ cytotoxic lymphocytes may damage the epidermal basal cells, leading to interface dermatitis, dyskeratosis, and highly inflammatory mucous-membrane disease.
Cummins DL et al. Lichenoid paraneoplastic pemphigus in the absence of detectable antibodies. J Am Acad Dermatol 2007 Jan; 56:153-9.
Comment
All four patients received rituximab prior to onset. Rituximab inhibits B cells and antibody production, although total levels of serum IgG were normal after treatment in the two patients tested. Perhaps rituximab somehow knocked out the humoral autoantibody response but left the cell-mediated ones intact. Perhaps rituximab itself caused the T-cell attack. Perhaps the patients had lichenoid mucositis from another cause (e.g., lichenoid drug reaction, chronic ulcerative stomatitis, Basex syndrome, erythema multiforme, or occult graft-versus-host disease).
Although, as Shakespeare suggests, “a rose by any other name would smell as sweet,” how would we know it was a rose without smelling it? Is lichenoid paraneoplastic pemphigus without acantholysis and autoantibodies really pemphigus? Fortunately, further study will likely resolve this issue. For example, longitudinal studies of patients with “ordinary” paraneoplastic pemphigus treated with rituximab may show that they lose their autoantibodies and acantholytic disease but maintain their cell-mediated immune reaction and lichenoid interface disease.