The Patient Global Assessment of Disease Activity in Rheumatoid Arthritis: Identification of Underlying Latent Factors

INTRODUCTION: The patient global assessment of disease activity is a crucial component of various measures of disease activity in rheumatoid arthritis (RA). Our objective was to identify underlying latent traits driving the patient global assessment using a quantitative, multivariable data reduction approach. METHODS: This was a prospective cross-sectional study of consecutive patients with RA. The patient sample was stratified to include 50 patients with patient-provider discordance (i.e., at least 25-mm absolute difference between the patient and provider global assessments) and 20 patients with patient-provider concordance (i.e., less than 25-mm absolute difference between the patient and provider global assessments). Data were collected from the most recent rheumatology visit, including patient characteristics, current RA medications, and comorbidities. Participants completed several validated patient-reported outcome measures. The data were evaluated using factor analysis, and then linear regression was used to determine the variability in the patient global assessment explained by the factor scores. RESULTS: The study included 70 patients with mean age of 61 years, 73% female, and with mean disease duration of 8 years. The means (SD) for the patient and provider global assessments were 44.6 (22.7) and 20.1 (17.7), respectively. Factor analysis yielded eight factors that represented measurements of pain, fatigue, depression or anxiety symptoms, prior diagnosis of depression or anxiety, advanced age and degenerative arthritis, inability to participate, fibromyalgia (clinical diagnosis and Widespread Pain Index), and undetermined. Linear regression analysis showed that fibromyalgia explained the greatest proportion of the variance in the patient global assessment followed by the other factors. CONCLUSION: Latent factors underlying the patient global assessment include pain, depression and anxiety, inability to participate, fibromyalgia, advanced age, and degenerative arthritis.