Measuring disease activity in patients with early rheumatoid arthritis

Current treatment strategies for rheumatoid arthritis (RA) aim to suppress the patient’s disease activity as early as possible. This requires valid and reliable measurements of disease activity. The DAS28 (Disease Activity Score for 28 joints) is an index measure that combines a 28‐tender joint count, a 28‐swollen joint count, a laboratory measure of inflammation (either the ESR or the CRP), and a patient‐reported feeling of general health (VAS-GH) into a single measure of disease activity. Though the DAS28 is frequently used, several concerns have been expressed. First, disease activity in omitted joints. Since assessing all joints is unfeasible, 28 joint counts (of the hands, wrists, elbows, shoulders, and knees) have been proposed. Although our studies showed that the inclusion of forefoot joints did not significantly improve the measurement range nor the measurement precision of the joint counts, these joints were frequently affected. This suggests that the assessment of omitted joints can be important when monitoring the disease trajectory of individual patients. Second, the interchangeable use of the ESR and CRP. Acute phase reactants are commonly used to quantify the severity of inflammation in RA. However, elevated concentrations of these reactants can be due to both the rheumatic disease and external factors like a patient’s age and sex. Hence, these external influences should be taken into account. We also showed that the DAS28‐CRP tends to yield lower scores than the DAS28‐ESR. Therefore, their scores cannot be used interchangeably. Third, the inclusion of the VAS-GH. Our analyses showed that the patient-reported VAS-GH has a poor reliability. Furthermore, its relatively low weighting within the DAS28 was decreased even further after weight optimization. Therefore, alternative, more reliable, patient‐reported outcome measures should be explored to incorporate the patient perspective on disease activity within the DAS28. This thesis shows that the DAS28 is a fairly reliable measure. While it gives good estimations of disease activity on a population level, inconsistencies can occur on an individual level. It is important to interpret DAS28 scores within their context, including both disease related and non‐disease related factors. Even though the DAS28 can guide the treatment process in clinical practice, a thorough inquiry of clinical and patient‐reported symptoms remains important.