Floor-pattern salt-split skin cannot distinguish bullous pemphigoid from epidermolysis bullosa acquisita. Use of toad skin.

BACKGROUND AND DESIGN: Patients with epidermolysis bullosa acquisita (EBA) and bullous pemphigoid (BP) can present with similar clinical features. These antigens have different phylogenetic origins. It was thought that sodium chloride split-skin immunofluorescence could reliably distinguish between BP and EBA. However, it has now been recognized that both diseases can present with a floor pattern fluorescence on salt-split skin. A simple method is required to distinguish these diseases. RESULTS: Serum specimens from two patients presenting with pruritic blisters showing a floor pattern immunofluorescence on salt-split skin were found to have positive fluorescence on toad skin that has the BP and not the EBA antigen. The diagnosis of BP in these patients was confirmed by a prompt response to treatment with systemic steroids. Electron microscopy showed a split at the lamina lucida. CONCLUSIONS: Bullous pemphigoid can present with a floor pattern immunofluorescence on salt-split skin. The use of the skin from invertebrates like the toad may help in distinguishing BP from EBA.