Pathergy Test in Thai Patients with Behcet's Disease : A Clinical, Histopathological and Direct Immunofluorescence Study

Objective: To evaluate the clinical, histopathological, and immunopathological findings of the pathergy test in Thai patients with Behcet's disease. Methods: A pathergy test using the needle prick method with a 20G disposable needle after cleaning with 70% alcohol was performed in 5 patients (4 females and 1 male), with Behcet's disease according to International Study Group (ISG) criteria. The skin was pricked making a 45o angle with the skin surface to a depth of 3 mm at an avascular and hairless point of both forearms symmetrically. After 4 and 48 hours, the test sites were evaluated clinically and skin biopsies were performed at a prick site on the right forearm after 4 hours for direct immunofluorescence study and after 48 hours at the prick site on the left forearm for histopathological study. Results: Clinical pathergy tests were positive (a single papular lesion at the needle prick site) in 3 out of 5 patients at 48 hours. No response was observed at 4 hours. Direct immunoflurorescence study showed no deposition of immnoglobulins (IgG, IgM, IgA) and C3 in any case. The histopathological findings 48 hours after the test revealed definite neutrophilic infiltration around a superficial vascular plexus in 4 cases, in addition, one of these had endothelial cell swelling with red blood cell extravasation. The rest (1 case) showed nonspecific findings. Conclusion: We conclude that a pathergy test is a useful tool for the diagnosis of Behcet's disease. The intradermal needle prick method using 20G disposable needle after cleaning the skin with 70% alcohol, yields results of moderately high sensitivity. The results should be evaluated at 48 hours both clinically and histopathologically.