The histopathology of pathergy: a chronologic study of skin hyperreactivity in Behçet's disease

Many patients with Behçet's disease (BD) demonstrate hyperreactivity (pathergy), and the induced skin lesions may serve as a model for the disease.

This study examined the sequence of histopathologic changes after needle prick trauma.

Eight patients fulfilling the International Study Group Criteria for Behçet's Disease, two patients with recurrent aphthous stomatitis, and two healthy controls each underwent intradermal injections with subsequent biopsies at 0, 4, 24, and 48 h. Hematoxylin and eosin sections were evaluated in a blinded fashion according to 11 histopathologic criteria.

At time zero, normal skin was seen. By 4 h, neutrophils were present usually admixed with lymphocytes (8 out of 10). The inflammatory cell density peaked by 24 h in 8 out of 10 patients and at 48 h in 2 out of 10 patients. Sparse leukocytoclasis was identifiable from 4 to 48 h, but was not associated with fibrin. True vasculitis (as evidenced by fibrin within vessel walls and/or intraluminal thrombi) was not seen. Intraepidermal pustules (IEPs) and polymorphonuclear (PMN) aggregates within the needle tract were seen as early as 4 h. The control patients and three out of eight of the BD patients failed to develop clinical lesions. Among this group histopathologic IEPs were lacking in all but two BD patients.

These data suggest that early pathergy is mediated by PMNs and lymphocytes without vasculitis. Hyperchemotaxis may explain the rapid accumulation of PMNs along the injection site.