Utility of serological assays in the diagnosis of paraneoplastic pemphigus.

BACKGROUND: Paraneoplastic pemphigus (PNP) is a rare autoimmune mucocutaneous blistering condition which has a universal association with malignancy and a poor prognosis. PNP, which is characterised by the presence of autoantibodies against plakins in the skin epithelial layer, can be a challenging diagnosis to make, particularly in those without an existing history of malignancy, as tissue biopsy findings may resemble other disorders that have similar clinical features. Thus, serology may be helpful in the diagnosis. Historically, indirect immunoflourescence (IIF) has been the most widely used assay in diagnostic laboratories with reasonable, but not ideal, specificity. Western blotting for various anti-plakin antibodies is more specific but not routinely available. Recently many antiplakin antibody specific assays have been developed commercially.

AIM: : The aim of our study was to compare the utility of three traditional assays, (IIF on rat bladder, monkey bladder and rat cardiac tissue) versus two newer plakin-based assays (envoplakin ELISA and HEK-transfected cell IIF) in patients presenting initially with oral ulceration alone.

METHOD: Fifty-nine samples [PNP n = 5, healthy controls n = 10, and disease controls n = 44, including pemphigus vulgaris (PV), mucous membrane pemphigoid (MMP), lichen planus (LP) and miscellaneous oral ulcers] were analysed on the five different assays and results were compared.

RESULTS: The current assay employed by our laboratory, rat bladder IIF, is the most sensitive assay for our three confirmed PNP cases (3/3, 100%), and has high specificity among all controls (53/54, 98.1%). The Envoplakin ELISA was even more specific (54/54, 100%), although less sensitive (1/3, 33.3%). Monkey bladder IIF had equal sensitivity to rat bladder IIF, although poorer specificity (51/54, 94.4%). Rat cardiac and HEK-transfected cell IIF performed the most poorly with 78-88% specificity, with the latter also having 0% sensitivity.

CONCLUSION: Our findings show that the newer envoplakin ELISA compares favourably with more traditional IIF in its high negative predictive value for PNP in both disease and healthy controls. However, traditional IIF seems to have superior sensitivity in our limited cohort of PNP patients.