1. Department of Rheumatology and Clinical Immunology, University Medical Centre Utrecht, Utrecht
2. Department of Internal Medicine and Rheumatology, Martini Hospital, Groningen
3. Department of Haematology, ErasmusMC, University Medical Centre Rotterdam, Rotterdam
4. Department of Rheumatology and Clinical Immunology, University Medical Centre Groningen, Groningen, The Netherlands Correspondence to: Maarten Limper, Department of Rheumatology and Clinical Immunology, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands. E-mail: m.limper-2@umcutrecht.nl