LAUSR

IgM: immunoglobulin M INTRODUCTION Bullous pemphigoid is an autoimmune blistering disease characterized by pruritus, tense blisters and erosions of the skin or mucosae, subepidermal splitting, and linear IgG or complement deposition along the epidermal basement membrane zone (BMZ), directed against the hemidesmosomal proteins BP180 and BP230. Deposition of IgA in conjunction with IgG is regularly found in bullous pemphigoid, whereas deposition of only IgA along the epidermal BMZ is known as linear IgA disease. The presence of only immunoglobulin M (IgM) deposition in pemphigoid has rarely been described and the relevance of IgM in the pathomechanism of autoimmune blistering diseases is still debated. In this case report, we describe a peculiar case involving a patient with bullous pemphigoid clinically, in which exclusively tissue bound and circulating IgM subclass antibodies were present, even after many years of disease activity and follow-up. This case provides more insight toward the possible role of IgM in the pathomechanism of bullous pemphigoid.