Diagnostic Utility of Immunofluorescence on Formalin-Fixed Paraffin-Embedded Skin Biopsy.

Background: When immunofluorescence on the frozen section is insufficient or unavailable, salvage immunofluorescence techniques can be used on formalin-fixed, paraffin-embedded tissue. The goal of the current investigation was to evaluate the diagnostic value of paraffin immunofluorescence following proteinase K digestion on skin biopsy samples in comparison to fresh frozen immunofluorescence. Materials and Methods: It was standardized and compared to the immunofluorescence on fresh frozen tissue (IF-Frozen) for paraffin immunofluorescence by proteinase K digestion of formalin-fixed paraffin-embedded skin biopsies (IF-FFPE). The study included 50 native skin biopsy cases, and fluorescein isothiocyanate-labeled IgA, IgG, IgM, and C3 intensity levels were evaluated in each case. Results: A total of 50 cases of native skin biopsy were included in the study, and their intensities for IgA, IgG, IgM, and C3 antibodies were compared. The average staining intensities in each disease group for the antibodies had equal intensity or had a minor difference (1+)/significant difference (2+). Paraffin immunofluorescence, proteinase K digestion had the best correlation, that is, had either equal or minor difference (1+) with fresh frozen immunofluorescence. The difference of 2+ intensity of antibodies between IF-FFPE and IF-Frozen was noted mainly in C3 antibody on paraneoplastic pemphigus. IF-FFPE showed a sensitivity of 100%, 97.6%, 100%, and 81.6% for IgA, IgG, IgM, and C3, respectively, whereas the specificity was 100% for IgA, IgG, IgM, and C3. Limitations: Small sample size and and the employment of one method of antigen retrieval in IF-FFPE. Conclusion: Immunofluorescence techniques done on formalin-fixed paraffin-embedded tissue can serve as salvage techniques in cases where immunofluorescence on the frozen section may not be adequate or may not be available.