Possible paraneoplastic syndrome case of bullous pemphigoid with immunoglobulin G anti‐BP180 C‐terminal domain antibodies associated with psoriasis and primary macroglobulinemia

A 61‐year‐old Japanese man developed bullous skin lesions during topical therapy for psoriasis vulgaris. Physical examination demonstrated numerous tense bullae and scaly erythemas on the trunk and extremities. Histopathology of the skin biopsy demonstrated subepidermal bullae and lymphocytic infiltration with eosinophils in the dermis. Direct immunofluorescence revealed linear deposits of immunoglobulin (Ig)G, IgA and C3 along the basement membrane zone. Indirect immunofluorescence of 1 mol/L NaCl‐split skin showed IgG reactivity with both epidermal and the dermal sides. IgM reactivity with both the epidermal and dermal sides was also detected. Enzyme‐linked immunosorbent assays showed negative results for both BP180 and BP230. Immunoelectrophoresis of serum and bone marrow aspiration revealed underlying primary macroglobulinemia with M‐proteinemia of IgM‐κ type. Immunoblot analysis revealed IgG, but not IgM, antibodies to recombinant protein of BP180 C‐terminal domain. We diagnosed the present case as bullous pemphigoid with IgG anti‐BP180 C‐terminal domain autoantibodies associated with primary macroglobulinemia and psoriasis vulgaris. Systemic administration of prednisolone 30 mg/day resulted in dramatic improvement of both bullous and psoriatic skin lesions. When the bullous and psoriatic lesions relapsed, DRC chemotherapy (dexamethasone, rituximab and cyclophosphamide) for macroglobulinemia was performed. Then, the psoriatic lesions improved and the bullous lesions disappeared. We suggested that the present case may be paraneoplastic syndrome of bullous pemphigoid associated with primary macroglobulinemia and psoriasis vulgaris.