Objective. There is no consensus on which comorbidity index is optimal for rheumatic health outcomes research. We compared a new Rheumatic Disease Comorbidity Index (RDCI) with the Charlson-Deyo Index (CDI), Functional Comorbidity Index (FCI), Elixhauser Total Score (ETS), Elixhauser Point System (EPS), and a simple comorbidity count (COUNT) using a US cohort of rheumatoid arthritis (RA) patients. Methods. Using administrative diagnostic codes and patient self-reporting, we tested predictive values of the RDCI, CDI, FCI, ETS, EPS, and COUNT for 2 outcomes: all-cause mortality and physical functioning. Indices were compared using 3 models: bare (consisting of age, sex, and race), administrative (bare plus visit frequency, body mass index, and treatments), and clinic (administrative plus erythrocyte sedimentation rate, nodules, rheumatoid factor positivity, and patient activity scale). Results. The ETS and RDCI best predicted death, with FCI performing the worst. The FCI best predicted function, with ETS and RDCI performing nearly as well. CDI predicted function poorly. The order of indices remained relatively unchanged in the different models, though the magnitude of improvement in Akaike's information criterion decreased in the administrative and clinic models. Conclusion. The RDCI and ETS are excellent indices as a means of accounting for comorbid illness when the RArelated outcomes of death and physical functioning are studied using administrative data. The RDCI is a versatile index and appears to perform well with self-report data as well as administrative data. Further studies are warranted to compare these indices using other outcomes in diverse study populations.

Objectives The co-occurrence of rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPA) is well described in rheumatoid arthritis (RA). However, the mechanisms underlying the potential interaction between these two distinct autoantibodies has not been well defined. We sought to evaluate the epidemiologic and molecular interaction of ACPA and RF with both disease activity as well as measures of RA-associated inflammation. Methods In a cohort of 1,488 Veterans with RA, measures of disease activity and levels of serum cytokines and multiplex ACPA were compared between the double-negative (aCCP-/RF-), ACPA-positive and RF-negative (aCCP+/RF-), ACPA-negative and RF-positive (aCCP-/RF+), or double-positive (aCCP+/RF+) subgroups. Studies were additionally performed using an in vitro immune complex (IC) stimulation assay in which macrophages were incubated with ACPA-ICs in the presence or absence of monoclonal IgM RF, and TNFα production measured as readout of macrophage activation. Results Compared with the double negative (as well each single positive) subgroup, the aCCP+/RF+ subgroup exhibited higher disease activity, serum CRP, and inflammatory cytokines (all P<0.001). In vitro stimulation of macrophages by ACPA-ICs induced increased cytokine production with the addition of monoclonal IgM RF as compared to ACPA-ICs alone (P=0.003) Conclusions The combined presence of ACPA and IgM RF mediates increased proinflammatory cytokine production in vitro, and is associated with increased systemic inflammation and disease activity in RA. Our data suggest that IgM RF enhances the capacity of ACPA-ICs to stimulate macrophage cytokine production, thereby providing a mechanistic link by which RF enhances the pathogenicity of ACPA-ICs in RA.

Mortality rates among US male veterans with RA are more than twice those of age-matched men in the general population. These results suggest that optimizing disease control, particularly with regimens that include MTX and minimize glucocorticoid exposure, could improve long-term survival in this population.