The many faces of epidermolysis bullosa acquisita after serration pattern analysis by direct immunofluorescence microscopy

Background The inflammatory variant of epidermolysis bullosa may mimic a form of pemphigoid. Objectives To estimate the frequency of epidermolysis bullosa acquisita (EBA) and bullous systemic lupus erythematosus (bSLE) among patients with subepidermal autoimmune bullous disease (sAIBD), and to correlate the isotype of in vivo antibody depositions to the clinical phenotype. Methods Patients with EBA or bSLE were systematically identified using serration pattern analysis by direct immunofluorescence microscopy in a prospective cohort of 364 patients with sAIBD. Correlation of the clinical phenotype to the isotype of the in vivo antibody depositions was investigated for 38 prospective and retrospective cases. Results The frequency of EBA or bSLE was 5.5% (n = 20), defined by the u-serration pattern, and reached only 1.9% (n = 7) when serological reactivity was the only criterion. The clinical phenotype of EBA was mechanobullous in 14 (37%) and inflammatory in 24 (63%) patients. Pure IgG-mediated cases (67%) were associated with the mechanobullous phenotype, whereas pure IgA-mediated cases (91%) were found more often in the inflammatory phenotype. Mucous membrane involvement was present in 22 (58%) patients, and neither correlated with IgG or IgA depositions, nor with a mechanobullous (64%) or inflammatory (54%) phenotype. Conclusions The frequency of EBA is about one in 18 among patients with sAIBD. The clinical phenotype in two of three cases is inflammatory, thus mimicking other sAIBDs, e. g. bullous pemphigoid, mucous membrane pemphigoid, or linear IgA disease. The yield of diagnosed EBA cases almost triples when serration pattern analysis is used by direct immunofluorescence microscopy on skin biopsy.