POS1373 THE DIAGNOSTIC ROLE OF PATHERGY TEST IN PATIENTS WITH BEHÇET’S DISEASE FROM WESTERN EUROPE

Abstract

Backgroundpathergy is the term used to describe the hyper-reactivity of the skin in response to a minimal trauma, as the consequence of an exacerbated response of the innate immune system [1]. Pathergy test has a central role for the diagnosis of Behçet’s disease (BD), especially in doubtful and atypical cases. However, while its incidence has been decreasing over the past few decades, there are significant variations in the frequency of pathergy among different geographic contexts [2]. These aspects affect the diagnostic role of pathergy test for patients with suspected BD.Objectivesto evaluate the frequency and features of positive pathergy test (PPT) in Italy, its role in the diagnosis of BD, and any association with other BD-related manifestations.Methods29 BD patients, 15 patients with spondyloarthritis (SpA) and 19 healthy controls (HCs) underwent two types of pathergy test, which were performed on the hairless part of the volar forearm ipsilaterally: intradermal injection of 0.5 ml normal saline and intradermally needle soaked with fresh self-saliva. Both pricks were done with a monouse 25 gauge hypodermic needle inserted with a vertical approach at a depth of 5 mm into the skin. The needle was withdrawn with a twisting movement. Skin reactions were observed 48 hours after prick. The results of pathergy tests were statistically analysed in the light of demographic, clinical, and therapeutic features of subjects enrolled. The BD activity at the time of the pathergy test was assessed with the Behçet’s Disease Current Activity Form (BDCAF) [3].Resultspathergy test performed with saline solution resulted always negative in all groups. Skin prick test using self-saliva resulted in the occurrence of a papule in 2 (6.9%) BD patients and in 1 (6.7%) patient with SpA. A ≥15 mm erythematous area surrounding the needle prick site was observed in 12 (41.4%) BD patients, in 4 (26.7%) patients with SpA (including the patient with the papule), and in 1 (5.6%) HCs (p=0.022). The frequency of skin erythema was significantly higher among BD patients compared to HCs (p=0.015); no statistically significant differences were observed between BD and SpA patients (p=0.53) as well as between SpA patients and HC (p=0.21). The occurrence of skin erythema was not associated with any of the BD-related clinical manifestations. No statistically significant differences were observed between BD patients with positive and negative pathergy test according to sex (p=0.873); HLA-B51 positivity (p-value=0.461); age at the pathergy test (p=0.929); and disease duration at the pathergy test (p=0.487). The mean BDCAF was 1.33±0.65 among patients with PPT and 0.82±0.72 among patients with negative pathergy test (p=0.092). Erythema at self-saliva prick test showed a sensitivity of 41.4% (C.I. 23.52%-61.06%) and a specificity of 85.3% (C.I. 68.94%-95.05%); the positive likelihood ratio was 2.81 (C.I. 1.12-7.05) and the negative likelihood ratio was 0.69 (C.I. 0.49-0.96).Conclusionthis study confirms the lower frequency of PPT in Western European BD patients if considering the development of a papule or a pustule in the site of pathergy test. Conversely, the onset of a ≥15 mm erythematous area surrounding the prick site could be sufficient to unveil the hyper-reactivity of the innate immune system in BD patients from Western Europe. Pathergy test is not pathognomonic of BD, as its positivity can be also observed in other innate immune system disorders, as observed for SpA patients.