Abstract
BACKGROUND: Controversy exists in understanding the effects of age at onset and comorbidities in predicting rheumatoid arthritis (RA) response to biologic therapy. OBJECTIVE: The objective of this study was to investigate the influence of age at onset and number of comorbidities on Health Assessment Questionnaire-Disability Index (HAQ-DI) and Clinical Disease Activity Index (CDAI) responses in active RA patients after 6 months of treatment with etanercept. METHODS: One thousand eight hundred ninety-nine RA patients were assessed after 6 months of etanercept therapy. Patients met the following inclusion criteria: initiated etanercept, continued therapy for at least 6 months, and were not in CDAI low disease activity (LDA) at baseline (CDAI ≤10.0). Changes in HAQ-DI and CDAI scores over 6 months were analyzed across age of onset quintiles. Multivariate regression models evaluated the independent association between both age at onset and number of comorbidities with change in HAQ-DI/CDAI scores or achieving LDA, while accounting for other covariates. RESULTS: Significant improvements in HAQ-DI and CDAI scores were observed in all age-onset groups, although HAQ-DI improvements were less in older-onset patients. Results of multiple linear regression demonstrated that younger age at onset, higher baseline HAQ-DI/CDAI score, rheumatoid factor positivity, shorter disease duration, and fewer comorbidities at baseline were independently associated with improvement in both HAQ-DI and CDAI scores. Similarly, achieving CDAI LDA after 6 or more months of etanercept was associated with younger age at onset, higher baseline CDAI, shorter disease duration, and fewer comorbidities. CONCLUSIONS: These patients with older-onset RA and more comorbidities clinically improved with etanercept, but had lower odds of achieving CDAI LDA. Age of onset and number of comorbidities may be important in determining RA tumor necrosis factor inhibitor response.