A hypocomplementemic vasculitic urticarial syndrome. Report of four new cases and definition of the disease.

We describe four new patients with a unique syndrome of persistent urticaria, with leukoclastic angiitis, severe angioedema, occasional life-threatening laryngeal edema, arthritis, arthralgia, neurologic abnormalities and pronounced persistent hypocomplementemia. The complement abnormalities involved markedly reduced levels of the Clq subunit of the first component of complement (Cl) in the presence of near normal levels of Clr and Cls subunits of Cl; modest to marked depletion of the fourth component of complement (C4), the second component of complement (C2) and the third component of complement (C3); and normal levels of the fifth through ninth components of complement (C5 through C9) and properdin factors B and D. A striking serologic abnormality found in all patients was the presence of low molecular weight (7S) proteins which precipitated with Clq in agarose gels; these previously were shown to be comprised at least in part of immunoglobulin G. The present experience is offered to help to define the clinical, histopathologic and serologic characteristics of this entity, designated hypocomplementemic vasculitic urticarial syndrome, and to emphasize its distinctiveness and prevalence.