False-positive intercellular indirect immunofluorescence test due to anti-blood group antibodies in a patient with epidermolysis bullosa acquisita

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We report a case of an epidermolysis bullosa acquisita (EBA) patient with a unique immunofluorescence pattern. The patient had pruritic erythematous plaques and tense blisters. Histopathological examination showed a subepidermal blister without acantholysis. Salt-split direct immunofluorescence demonstrated clear linear IgG and C3 deposition along the dermal side of the basement membrane zone; this deposition is characteristic of EBA. Indirect immunofluorescence (IIF) using monkey esophagus mucosa as substrate showed intercellular IgG deposition throughout the epidermis, which suggested pemphigus. After absorption with erythrocytes of blood group AB, the patient's serum showed no deposition in IIF. We reviewed the literatures regarding false-positive intraepidermal immunofluorescence staining due to cross-reactivity of ABO blood group antibodies and suggest that this possibility should be considered in cases with conflicting immunofluorescence patterns.

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