[The sterile Behçet pustule: a typical skin manifestation of the Behçet syndrome].

Solitary pustules were excised from five patients with Behçet's syndrome and examined histologically, immunohistologically, and--in one case--by immunoelectron microscopy. Histologically the changes were largely confined to the venules of the middle and lower corium. The endothelium was swollen, in part the vascular walls were destroyed. In the perivascular spaces there was round-cell infiltration, mixed with numerous neutrophilic granulocytes, some of them disintegrated. Immunofluorescence-microscopy revealed perivascular deposition of complement C3 and C1q. In fresh lesions there were also IgG or IgM precipitates. Immuno-electron microscopy also demonstrated complement C3 subendothelially. Fibrin deposition and disintegrating neutrophilic granulocytes marked the leukocytoclastic vasculitis. Taken together the findings indicate that an immune-complex vasculitis takes part in the pathogenic mechanism of pustule formation in Behcet's syndrome.