Urticarial vasculitis associated with a monoclonal IgM gammopathy: Schnitzler's syndrome.

We describe two cases of Schnitzler's syndrome presenting with urticarial vasculitis, in which there was a monoclonal IgM of kappa light-chain isotype. Skin histology showed a perivascular leucocytic infiltrate and leucocytoclasis. One patient had an abnormal complement profile and positive rheumatoid factor while the other had antibodies to unidentified soluble nuclear antigens, anti-cytoplasmic antibodies and circulating immune complexes. In addition, in the first case deposits of IgM, C3 and, to a lesser degree, of IgG were observed in the walls of small blood vessels.