Use of IgG4 Immunohistochemistry as a Diagnostic Tool for Pemphigus

Pemphigus belongs to the group of antibody mediated autoimmune vesiculobullous disease (AIBD) of skin and mucous membranes. Antibodies are directed against the desmosomal adhesion proteins and IgG4 is the predominant subclass. It is a rare disease associated with significant mortality and morbidity. DIF is the gold standard test for AIBD. It requires fresh frozen section which is a major technical issue in most centres. The aim of this research was to study the diagnostic accuracy of IgG4 immunohistochemistry in pemphigus. The study was conducted as a diagnostic test evaluation in a tertiary care hospital. Paraffin blocks of histopathologically diagnosed AIBD were used for doing immunohistochemistry. The findings were compared with DIF findings. Statistical analysis was performed using SPSS, version 20.0. 48 paraffin blocks of AIBD were selected, DIF of all cases were already done from outside centre. There were 21 cases of pemphigus, 25 cases of bullous pemphigoid and one case each of epidermolysis bullosa acquisita and dermatitis herpetiformis. The sensitivity of IgG4 IHC was found to be 85.7%, specificity 96.3%, positive predictive value of 94.7% and negative predictive value 89.7%. So, we conclude that IgG4 IHC done on paraffin sections can be used as a diagnostic tool for pemphigus