Epidermolysis bullosa acquisita and anti-p200 pemphigoid as major subepidermal autoimmune bullous diseases diagnosed by floor binding on indirect immunofluorescence microscopy using human salt-split skin

Background: Subepidermal autoimmune bullous diseases are a diverse group of diseases with overlapping clinical and immunopathological features. Indirect immunofluorescence microscopy on artificially split skin helps to classify these conditions into those with staining on the epidermal side of the split ('roof-binding') and those with staining on the dermal side ('floor-binding'). Epidermolysis bullosa acquisita is the prototype of 'floor-binding' subepidermal autoimmune bullous diseases. However, not all floor-binding sera are associated with epidermolysis bullosa acquisita. Aim: The aim of this study was to evaluate the clinical and immunological profile of patients with floor-binding subepidermal autoimmune bullous disease by indirect immunofluorescence microscopy and to identify the target antigens in them. Methods: Ten patients who showed a floor-binding pattern were studied with regard to their clinical and immunopathological characteristics. Target antigens were identified by modified indirect immunofluorescence microscopy using recessive dystrophic epidermolysis bullosa skin, enzyme linked immunosorbent assay, and immunoblotting. Results: Diagnosis of epidermolysis bullosa acquisita was confirmed in six patients. Three patients with an inflammatory subepidermal autoimmune bullous disease mimicking bullous pemphigoid reacted with a 200 kDa protein on immunoblotting with dermal extract, as is characteristic of anti-p200 pemphigoid. One serum showed both roof and floor binding, and reacted with the BP180 antigen. Limitation: We could not perform serration pattern analysis in our patients. Conclusion: In this study, we report three cases of anti-p200 pemphigoid from India. These cases, though indistinguishable clinically from bullous pemphigoid, revealed a floor-binding pattern on indirect immunofluorescence using salt-split skin.