1. St. Elisabeth-Hospital Meerbusch-Lank, Dept. Rheumatology, Meerbusch, Germany
2. Clinic for Rheumatology, University Hospital Düsseldorf, Medical Faculty of Heinrich Heine University, Düsseldorf, Germany
3. Hiller Research Unit, University Hospital Düsseldorf, Medical Faculty of Heinrich Heine University, Düsseldorf, Germany
4. Medical Biometry and Epidemiology, Faculty of Health, Witten/Herdecke University, Witten, Germany