1 Department of Internal Medicine, Division of Vascular Medicine, University of Groningen, University Medical Center Groningen.
2 Department of Rheumatology and Clinical Immunology, University of Groningen, University Medical Center Groningen.
3 Department of Internal Medicine, Division of Vascular Medicine, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands. d.j.mulder@umcg.nl.