Evaluation of a newly available ELISA for envoplakin autoantibodies for the diagnosis of paraneoplastic pemphigus

IMPORTANCE: Paraneoplastic pemphigus (PNP) is routinely diagnosed by the presence of autoantibodies for desmoplakin by indirect immunofluorescence (IIF) on rat bladder epithelium (RBE). IIF on RBE has recently been found to be positive in select cases of other blistering disorders. A new ELISA that detects envoplakin autoantibodies has recently been developed for the diagnosis of PNP. In this study, we measure the specificity of IIF on RBE and compare it to the new ELISA. OBSERVATIONS: We measured the specificity of IIF on RBE to be 86% which is on the lower end of the previously reported specificity of 83% to 98.9%. The ELISA for envoplakin autoantibodies has a technical sensitivity of 100%, diagnostic sensitivity of 83%, and specificity of 91%. CONCLUSIONS AND RELEVANCE: This ELISA for envoplakin autoantibodies is now commercially available and technically easier to perform then the immunoblot. We recommend that this new ELISA serves as a confirmatory test in cases of a positive IIF on RBE given its higher specificity.