Chronic urticaria as a manifestation of necrotizing venulitis.

In a group of patients with a syndrome consisting of recurrent episodes of urticaria, arthralgia, abdominal pain, and (rarely) glomerulonephritis, examination of skin biopsy specimens showed necrotizing venulitis. An elevated erythrocyte sedimentation rate was the most common laboratory abnormality. Analyses of serum immunoglobulins revealed random abnormalities of immunoglobulin levels, and assessment of the complement system showed two groups of patients--some with hypocomplementemia and others with a normal complement system. In those with hypocomplementemia, there were low levels of C1q, C4 and, occasionally, C3, compatible with activation of the classic complement pathway. Although the cause of this syndrome is unknown, the complement profiles suggest that more than one mechanism of vascular damage may be operative.