[Assessment of disease course in chronic rheumatoid arthritis: new quantitative dimensions for clinical practice]

Longterm follow-up of patients with rheumatoid arthritis requires systematic measurement of all relevant disease dimensions. The disease process can be measured reliably with the disease activity score (DAS) which integrates the erythrocyte sedimentation rate and the number of swollen and the number of tender joints out of 28 defined joints. Cumulatively the disease process may result in joint damage which can be measured with a radiological score averaging the level of destruction of 10 key joints. Synovitis and/or joint damage lead to reduced joint mobility and muscle strength which may be quantified using a muscle strength index (MSI) which integrates the information of isometric muscle strength of knee and elbow extension and flexion. The most important outcome dimensions are symptoms and physical functional disability, which can be measured comprehensively with a symptom-oriented rheumatoid arthritis disease activity index (RADAI) and the health assessment questionnaire (HAQ). Reduction of a wide range of information to a few valid indices representing all relevant disease dimensions allows interpretable but comprehensive evaluation of the disease course.