Urticarial vasculitis represents a spectrum of diseases characterized by urticaria and histopathologic evidence of leukocytoclastic vasculitis, the descriptive term for cutaneous vasculitis. There may be localized disease with minimal to severe urticaria and minimal to systemic vasculitis, which when extensive, may be associated with hypocomplementemia. Hypocomplementemic urticarial vasculitis syndrome (HUVS), also known as McDuffie syndrome, is a rare immune complex-mediated small vessel vasculitis characterized by urticaria, hypocomplementemia (low C1q, C3, and C4), and systemic manifestations, and it is also associated with circulating anti-C1q autoantibodies. It can have an initial presentation of an underlying systemic disorder, or systemic manifestations may develop thereafter. Common systemic manifestations involve the pulmonary, visual, musculoskeletal, and renal organs and can present as angioedema, arthralgia, chronic obstructive pulmonary disease (COPD), glomerulonephritis, Sjögren's syndrome, uveitis, or cryoglobulinemia. The most common association has been with systemic lupus erythematosus (SLE), but COPD and uveitis are also associated.

HUVS predominantly affects women more than men, with a ratio of 8:1. It rarely affects children. Its peak incidence is in the fifth decade, with an average age of presentation of 48 years.

Related topic: Urticarial vasculitis (discusses normocomplementemic form)