Pathergy test in Behcet's disease: change in incidence over the time

Introduction: Pathergy phenomenon (PP) is used as a criterion in many diagnostic criteria for Behcet's disease (BD): Curth, Japan, Hubault and Hamza, Cheng and Zhang, Dilsen, International Study Group, Iran criteria (traditional format and the Classification Tree), Korea criteria, and the new International Criteria. PP is rather specific to BD. It has been reported with high frequency from most countries along the Silk Road, but with much lower frequency from other countries (UK, US). The incidence of PP has been reported from some countries (Japan, Turkey) to decrease gradually. The aim of this study was to test the above hypothesis in a large cohort of patients in Iran. Materials: Patients (6057) were divided into several groups by two methods. Method 1: patients were divided into six groups according to the time of their first visit. Method 2: patients were divided into four groups according to the date of the beginning of their first manifestation. Results: In method 1, the percentage of PP was 71.8% from patients 1–1000. The percentage became 55.9% from patients 1001–2000, 57.6% from patients 2001–3000, 58.8% from patients 3001–4000, 45.3% from patients 4001–5000, and 33.9% from patients 5001–6000. In method 2, the percentage of PP was 61.5% for patients with their disease onset before 1977. The percentage was 59.9% for patients with their disease starting between 1978 and 1987. The percentage dropped to 52.1% for patients with disease onset between 1988 and 1997. The percentage finally dropped to 41% for patients having their disease onset between 1998 and 2007. Conclusion: The incidence of PP is decreasing gradually. It is now 34%, which is rather low for a criterion used in many diagnosis criteria. It is important to find a surrogate for it because with the decrease in the incidence of PP the sensitivity of the diagnosis criteria will drop significantly.