Is a Fundamental Change in the Interpretation of Rheumatoid Arthritis Disease Activity Necessary?

Disease Activity Score (DAS) composite models are moderately precise and robust measures of disease severity when they are used in rheumatoid arthritis (RA) cohorts. They are less so when used for individual patients. This is because subjective components, patient global assessment of well-being and tender joint count, modified by factors other than RA biological disease activity, often obfuscate interpretation of disease activity. Comorbidities, especially distress, can disproportionately inflate these components. Fibromyalgia, essentially synonymous with distress, pain augmentation, and depression, is a common comorbidity. Its presence and severity can be determined by the Polysymptomatic Distress Scale (PSD). The differential effects of distress and fibromyalgia syndrome on the DAS can be demonstrated by manipulating information already there: the arithmetic differences or ratios of the tender joint count and swollen joint count and comparison of the modified disease activity score with 28 joints to the disease activity score with 28 joints-patient (DAS28-derived indices that measure the contribution of the relatively objective or relatively subjective components, respectively). The potentially more objective multibiomarker disease activity might also be used to test the severity of biological RA disease activity. These tools may be used to elucidate disproportionate values for subjective DAS model components, which then should facilitate identification of the underlying process factors, including depression, for potential treatment.