Background : Leukocytoclastic vasculitis (LCV) is a clinico-pathological entity. Previous direct immunofluorescence study (DIF) studies of vasculitis showed positive findings mainly in the early stage of the disease.
Objective : To study the positive yield and patterns of DIF in patients with various stages of LCV.
Design : One hundred patients with LCV who attended the Department of Dermatology, Siriraj Hospital from 1997 to 2000 were enrolled in the study.
Results : The study showed immunoreactive deposits in blood vessel walls in 76 cases(76%). Forty seven percent of patients showed immunoreactant deposit only in superficial blood vessel walls, 3% had deposits only in deep blood vessel walls. Superficial and deep blood vessel wall deposits were seen in 26%. Dermoepidermal deposit in addition to blood vessel wall deposit was found in 39%. The most common immunoreactive
deposit was C3 (71%), followed by IgM (35%), IgA (12%) and IgG (8%) respectively. The age of the skin lesions at the time of biopsy ranged from 1 to 7 days. 82% of patients with one day old lesions showed immunoreactive deposits in the blood vessel walls and 74% of the group with lesions aged 2-7 days at the
time of biopsy showed immunoreactive deposits in the blood vessel walls.
Conclusion : The present study showed a 76% positive yield for DIF study in patients with LCV when biopsies were performed within one week of onset. There was a tendency for the percentage of positive DIF results to decline when the biopsy was performed on lesions that were more than 1 day old.

Keywords : Vasculitis, Immunofluorescence