Acquired immunobullous disease: a cutaneous manifestation of IgM macroglobulinaemia.

Waldenström's macroglobulinaemia has been associated with a variety of cutaneous manifestations. We report a patient with an acquired bullous disorder associated with skin fragility and IgM kappa paraprotein. Immunofluorescence studies demonstrated bright linear deposition of IgM along the basement membrane zone (BMZ), around dermal blood vessels and on arrector pili muscles. Weak keratinocyte cell surface staining with IgM was also noted. There was no deposition of complement or other immunoglobulins. Indirect immunofluorescent studies revealed a circulating IgM anti-BMZ antibody (titre 1/200), which bound to both the roof and the floor of a 1 mol/l NaCl split skin substrate. Immunoblotting analysis of the patient's serum, with both epidermal and dermal extracts, was negative. Treatment with a combination of prednisolone and azathioprine was successful. We suggest that this IgM kappa paraprotein has a low affinity for an undefined epitope within the lamina lucida, which has produced a subepidermal bullous disorder associated with skin fragility.