POLISH ARCHIVES OF INTERNAL MEDICINE 2018; 128 (3) 148 prevalence rates among immigrants compared with native Europeans. In the October 2017 issue of the Polish Archives of Internal Medicine (Pol Arch Intern Med), Kanecki et al 7 reported the frst study from Poland on the incidence and prevalence of BS. Tis is actu‑ ally the frst prevalence study of BS from Eastern Europe, to the best of our knowledge. Te authors report an incidence rate of 0.5 per 1 000 000 per year (95% CI, 0.35–0.61) and a point prevalence of 0.34 per 100 000, which is the second low‑ est prevalence rate reported from Europe after Scotland. 8 Te low immigration rate from coun‑ tries with high prevalence of BS to Poland may be a contributing factor to this low prevalence, but it is still lower than that in native European populations reported in studies which give sepa‑ rate prevalence rates for natives and immigrants in that country. 4-6 A recent meta‑analysis emphasized that cau‑ tion is needed when interpreting and comparing the results of prevalence studies for BS. 2 Te au‑ thors estimated a 22‑fold higher pooled preva‑ lence for sample surveys (also called feld or pop‑ ulation surveys), compared with census surveys. Tis may be explained by the fact that BS has a variable disease course. Tis is especially true for the severity and frequency of the symptoms. Moreover, some symptoms such as oral apthous and papulopustular lesions are not rare in the gen‑ eral population, and all manifestations tend to ameliorate with aging. 9 Tus, mild cases and es‑ pecially those without major organ involvement may be underrepresented in census surveys. Tis may be even more pronounced in surveys based on hospitalization records. In the current study, which is also based on hospitalizations, the au‑ thors explain that systemic vasculitides with mul‑ tiorgan involvement such as BS are usually hos‑ pitalized since treatment, and advanced diagnos‑ tic procedures that can be done in inpatient set‑ tings may be required. However, this may still be a source of bias for underreporting. Prevalence studies are important for identify‑ ing the disease burden and planning health care needs for a condition, for determining the chang‑ es in disease prevalence in a country or a certain population over time, and for making compar‑ isons across diferent populations, which helps estimate how the results of a study in a certain country may be applicable to other countries in‑ dicating the generalizability of the results. More‑ over, such epidemiology studies may provide clues for pathogenesis by pointing to the role of cer‑ tain genetic or environmental factors. Te key issue in conducting good prevalence studies is the choice of the right sample, right methodolo‑ gy, and right analysis. 1 Several prevalence studies have been conducted for Behçet syndrome (BS) in diferent parts of the world, with diferent ap‑ proaches regarding each of these points. Difer‑ ences such as community‑based versus hospital‑ ‑based studies, diferences in the criteria used for defning patients with BS, such as the Interna‑ tional Study Group (ISG) criteria or the Interna‑ tional Criteria for Behçet’s Disease (ICBD) crite‑ ria, and the use of prevalence rates or prevalence odds ratios may render the interpretation and comparison of these studies difcult. 2 BS is more prevalent along the ancient Silk Route where the prevalence of HLA‑B51 is high. Te highest prevalence is in Turkey (420 per 100 000), followed by Iran (80 per 100 000), Iraq (17 per 100 000), Japan (7–13.5 per 100 000), and China (2.6 per 100 000). Te estimated prev‑ alence of BS varies across European countries, ranging between 0.3 and 27 per 100 000 and is higher in the southern parts. 3 It was thought that immigration may be a cause of increased BS prevalence in European countries. In a study from Germany that elaborates on this issue, the prevalence of BS was 1.47 per 100 000 among Germans and 77 per 100 000 among Turks liv‑ ing in Germany. 4 Similarly, 2 other studies from Sweden (13.6 vs 2.0 per 100 000) 5 and France (6.2–36.4 vs 2 per 100 000) 6 found higher EDITORIAL Considerations in designing and interpreting prevalence studies for Behçet syndrome Gulen Hatemi, Sinem Nihal Esatoglu, Sebahattin Yurdakul Division of Rheumatology, Department of Internal Medicine, Cerrahpasa Medical Faculty, Istanbul University, Istanbul, Turkey Correspondence to: Gulen Hatemi, MD, Division of Rheumatology, Department of Internal Medicine, Cerrahpasa Medical Faculty, Istanbul University, Stanbul Üniversitesi Cerrahpaşa Tıp Fakültesi, 34098 Cerrahpaşa-Fatih/ İstanbul, phone: +90 212 4143 000, email: gulenhatemi@yahoo.com Received: December 5, 2017. Accepted: December 5, 2017. Published online: March 29, 2018. Conflict of interest: none declared. Pol Arch Intern Med. 2018; 128 (3): 148-149 doi:10.20452/pamw.4233 Copyright by Medycyna Praktyczna, Kraków 2017