Immunohistochemical diagnosis of mucous membrane pemphigoid

BackgroundMucous membrane pemphigoid (MMP) is an autoimmune subepithelial blistering disease with predominant involvement of mucosal surfaces. It is usually diagnosed by direct immunofluorescence microscopy of frozen biopsies, demonstrating linear deposits of complement, IgG or IgA along the basement membrane. The aim of this study was to investigate the utility of immunohistochemistry on formalin-fixed, paraffin-embedded tissue biopsies for the diagnosis of MMP and to compare its sensitivity to that of direct immunofluorescence microscopy. MethodsWe examined 50 biopsies from 34 patients with immunologically confirmed MMP by immunohistochemistry for C3d, C4d, IgG and IgA. ResultsLinear deposits of C3d were detected in 46% of biopsies, and 53% of patients had at least one biopsy positive for C3d. Linear deposits of C4d were detected in 52% of biopsies and 59% of patients had at least one biopsy positive for C4d. Overall, 56% of biopsies and 68% of patients were positive by either C3d or C4d or both stainings. The sensitivity of either staining in mucosal biopsies was lower than in skin samples. Basement membrane deposits of IgG or IgA could not be detected in any biopsy. ConclusionsOur findings demonstrate that immunohistochemistry for C3d or C4d is a helpful screening procedure for cases of suspected MMP where frozen tissue is not readily available. Negative findings, however, do not exclude a possible diagnosis of MMP and should prompt an additional biopsy for direct immunofluorescence studies. Immunohistochemical detection of IgG or IgA cannot yet be used for the diagnosis of MMP.