Background: Paraneoplastic pemphigus is a blistering disease with specific serum immunoprecipitation findings. Although immunoprecipitation studies allow accurate diagnosis, they are time-consuming, expensive, and not readily available. In contrast, indirect immunofluorescence (IIF) testing of serum on transitional rat bladder epithelium is a simple and inexpensive method available to any immunopathology laboratory. Objective: Our purpose was to determine the specificity of positive IIF on rat bladder epithelium for paraneoplastic pemphigus. Methods: The IIF findings in four index cases of paraneoplastic pemphigus were compared with the findings in 47 patients with a variety of malignant neoplasms and no associated blistering disease as well as 49 patients with vesiculobullous or lichenoid disease but no neoplasia. Results: IIF was negative in all patients with neoplasia and no blistering disease and negative in all but one of the patients with vesiculobullous or lichenoid disease without neoplasia (98.9% specificity). Conclusion: IIF on transitional rat bladder epithelium appears to be a highly specific test for paraneoplastic pemphigus. Because of its simplicity and inexpensiveness, we suggest that IIF be performed on transitional epithelium in any suspected case of paraneoplastic pemphigus.
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