Danish researchers report that rheumatoid arthritis patients’ baseline patient global score component of the Disease-Activity Score–28 tool was most strongly correlated with patient-reported outcomes and was the best predictor of a gain in quality adjusted life years following 1 year of biological therapy in a prospective observational study.
An objective C-reactive protein (CRP) measure, however, had no predictive value, and no sharp demarcation between objective and subjective variables was apparent.
The finding that patient global score at baseline may drive a gain in quality adjusted life years (QALY) could improve understanding of which disease-related factors might affect the cost per QALY gains (an important measure for comparing the cost-effectiveness of treatments) and predict treatment response, according to Dr. Louise Linde of the DANBIO Registry, Glostrup, Denmark, and her colleagues (J. Rheumatol. 2013;40:1479-86).
Of 282 patients who completed the study, 68% gained QALYs following 1 year of biological therapy (mean of 0.14), 61% were European League Against Rheumatism (EULAR) criteria responders, and 62% achieved minimally important differences based on the European Quality of Life 5 Dimensions (EQ-5D) questionnaire.
The proportion of patients achieving both a EULAR and EQ-5D response was 55%. Cross-tabulation by response groups (EULAR response/EQ-5D response, EULAR no response/EQ-5D no response, EULAR response/EQ-5D no response, and EULAR no response/EQ-5D response) showed that the mean reduction in swollen joints across the groups ranged from 0 to 6 with clinically and statistically significant differences in three of six possible comparisons.
Similar patterns were seen for tender joints and patient global score, the investigators said.
"Thus, the mean reduction in tender joints ranged from –1 to 9 across the response groups. In addition, the EULAR no response/EQ-5D response group could be discriminated from the EULAR response/EQ-5D response group, leading to significant differences (3-9 tender joints) in four of six comparisons. Similarly, the mean reduction in patient global score ranged from –0.7 to 4.0 cm across the response groups, and highly significant differences of 2.0-4.7 cm were observed between the response groups in five of six comparisons," they said.
However, the mean reduction in CRP, which ranged from 6.0 to 16.5 mg/L across the response groups, distinguished only the EULAR response/EQ-5D response from the EULAR nonresponders.
All EULAR responders experienced significant reductions in swollen and tender joints, CRP, and patient global scores – regardless of EQ-5D status – and the EULAR nonresponders who had an EQ-5D response experienced similar improvements. However, those with no EQ-5D response experienced a worsening in patient global score of 0.7.
Patient global score was strongly correlated with responses on both the EULAR and European Quality of Life 5 Dimensions EQ-5D.
Regression analysis demonstrated that "the gain in QALY after 1 year of biological therapy increased with increasing baseline patient global score and number of swollen joints, and patients with two or more extraarticular manifestations gained more QALY compared with those without such manifestations," the investigators wrote.
"This finding may reflect the likely scenario that patients with very active or severe disease have more room for improvement. This does not imply, however that such patients will have a more favorable final status than those with less active or less severe disease at baseline, a conclusion not supported by our observational data," they noted.
The mean age of the patients in this study was 55 years. They were recruited from 17 routine care sites between November 2005 and July 2007. Clinical and patient-reported data were collected at baseline and after 3, 6, and 12 months of therapy. Clinical data were obtained via the Danish DANBIO registry, which includes 90% of Danish patients with RA who are receiving biological therapy. Collected clinical data included disease duration, 28 swollen and tender joint counts, CRP, patient global score on a visual analog scale, IgM-rheumatoid factor status, number of previous biological therapies, and concomitant use of methotrexate and glucocorticoids. Self-reported patient data included marital status, education, smoking behavior, body mass index, exercise habits, extra-articular features, joint surgery, and comorbidities.
In addition to the EQ-5D, participants also completed the validated Danish Health Assessment Questionnaire.
Though limited by the factors inherent in observational study design, the study is strengthened by the nationwide recruitment, the fact that is was carried out in a clinical setting, and the fact that the study population had similar baseline demographic, clinical, and patent-reported values as have been reported for other RA patients treated with biological therapies in routine care in several other registries.
"This result suggests that our findings may be generalizable to patients with RA treated in routine care with biologicals in countries with a public healthcare system similar to the Danish model," the investigators wrote.