Hypocomplementemic Urticarial Vasculitis (Anti-C1q Vasculitis)

Urticarial vasculitis (UV) is a clinicopathological condition characterized by recurrent episodes of urticaria lasting for more than 6 months, with fixed pruritic and painful lesions persisting longer than 24 h, and histopathology demonstrating leukocytoclastic vasculitis. Hypocomplementemic UV (HUV) and normocomplementemic UV (NUV) are the two differentiated forms of UV. While NUV is considered a cutaneous single-organ vasculitis, HUV or anti-C1q vasculitis has been recognized as an immune complex vasculitis affecting small vessels presenting with urticarial lesions, hypocomplementemia, and systemic extent. Extracutaneous manifestations include articular complaints, uveitis, and recurrent abdominal pain. However, renal and pulmonary involvement as glomerulonephritis and chronic obstructive pulmonary disease (COPD) are also common and associated with bad prognosis. The presence of circulating anti-C1q antibodies, and complement and immunoglobulins (Ig) deposits in or around the walls of small vessels at direct immunofluorescence constitute distinctive laboratory and immunological findings in HUV. Although HUV can be idiopathic, it can also occur associated with autoimmune diseases, infections, reactions to medications, or as a paraneoplastic syndrome. A differential diagnosis with these and other conditions presenting with urticarial lesions is mandatory. Treatment should be tailored according to the predominant clinical presentation. Smoking cessation is crucial. For cutaneous lesions, antihistamines, colchicine, dapsone, hydroxychloroquine, or low doses of glucocorticoids can be useful. In systemic forms with renal and/or pulmonary involvement, glucocorticoids have been used, usually accompanied by cyclophosphamide and other conventional immunosuppressive drugs. Recently, biologic drugs, such as anti-CD20, anti-interleukin 1, and anti-IgE agents, have been found effective in refractory cases.