The Nijmegen inception cohort of early rheumatoid arthritis.

Rheumatoid arthritis is a heterogeneous chronic disease with an unpredictable disease course. To study such a disease, longterm observational studies are needed, with regular assessment of patients using valid and reproducible measures. This article describes the purpose and design of such a study at the Department of Rheumatology, University Medical Centre Nijmegen. Within this inception cohort, several instruments to assess RA were developed and validated, such as the Disease Activity Score, the European League Against Rheumatism response criteria, and a Dutch version of the Health Assessment Questionnaire disability index. These instruments are described and results of studies are discussed concerning prognostic and predictive factors, disease course, and the relationship between the different process and outcome measures.