Psoriasis bullosa acquisita.

We report a 51-year-old man with a 20-year history of chronic plaque psoriasis who developed an autoimmune subepidermal blistering eruption that had clinical features of bullous pemphigoid, erythema multiforme and epidermolysis bullosa acquisita. Investigations revealed a 1 : 400 titre circulating and in vivo bound IgG autoantibody that mapped to the dermal side of 1 m NaCl-split skin and localized to the lower lamina lucida/upper lamina densa on immunogold electron microscopy. Immunoblotting, using dermal extracts, showed serum binding to antigens of approximately 200- and approximately 260 kDa. Indirect immunofluorescence microscopy, using the patient's serum on archival skin sections taken from selected individuals with different forms of inherited epidermolysis bullosa as substrate, showed normal basement membrane labelling on all samples apart from recessive dystrophic epidermolysis bullosa skin (with inherent mutations in the type VII collagen gene): in these cases there was a complete absence of immunostaining. Clinically, the patient responded rapidly to combination treatment with intravenous immunoglobulin and oral corticosteroids, dapsone and mycophenolate mofetil. Autoimmune subepidermal blistering has been reported in other patients with psoriasis, although no specific target antigen has ever been determined. Our study provides preliminary evidence that, for this patient at least, the autoantibody may be targeted against a skin component closely associated with type VII collagen (the epidermolysis bullosa acquisita antigen). Therefore, we propose the term 'psoriasis bullosa acquisita' for this and possibly other patients with similar skin eruptions.