Objective. The US national prevalence of spondylarthritis (SpA) was estimated for 2 published sets of classification criteria: the Amor criteria and the European Spondylarthropathy Study Group (ESSG) criteria. These 2 SpA criteria sets have been the most widely utilized in previous population-based studies of SpA.Methods. The US SpA prevalence estimates were based on a representative sample of 5,013 US adults ages 20-69 years who were examined in the US National Health and Nutrition Examination Survey (NHANES) 2009-2010.Results. The overall age-adjusted prevalence of definite and probable SpA by the Amor criteria was 0.9% (95% confidence interval [95% CI] 0.7-1.1%), corresponding to an estimated 1.7 million persons (95% CI 1.4-2.1 million persons). The age-adjusted prevalence of SpA by the ESSG criteria was 1.4% (95% CI 1.0-1.9%), corresponding to an estimated 2.7 million persons (95% CI 1.9-3.7 million persons). There were no statistically significant sex differences in SpA prevalence. The SpA prevalence among non-Hispanic white persons was 1.0% (95% CI 0.7-1.5%) by the Amor criteria and 1.5% (95% CI 1.0-2.3%) by the ESSG criteria. SpA prevalence could not be reliably estimated in other race/ethnicity subgroups due to sample size imitations.Conclusion. The SpA prevalence estimates are in the range of SpA prevalence estimates reported elsewhere in population-based surveys and it is likely that SpA may affect up to 1% of US adults, a prevalence similar to that reported for rheumatoid arthritis. The current US SpA prevalence estimates may be lower than the true value because the NHANES 2009-2010 data collection did not capture a complete set of the elements specified in the 2 SpA criteria sets.

Objective To estimate the current US inflammatory back pain (IBP) prevalence using four published case definitions. Methods Analysis of an IBP data collection instrument specifically designed for the 2009–10 National Health and Nutrition Examination Survey. Subjects were 5103 US adults ages 20–69 with complete data. IBP prevalence as determined by Calin et al criteria, European Spondylarthropathy Study Group (ESSG) criteria, and Berlin criteria 8a and 7b. Results Age-adjusted US prevalence of IBP by Calin criteria was 5.0% (95% CI 4.2% to 5.8%). Prevalence of IBP was 5.6% (95% CI 4.7% to 6.5%) by ESSG criteria, and 5.8% (95% CI 5.2% to 6.4%) and 6.0% (95% CI 4.9% to 7.1%) by Berlin Criteria 8a and 7b, respectively. IBP prevalence did not differ significantly by age groups or between men and women. IBP prevalence was significantly lower among non-Hispanic black persons compared with non-Hispanic white persons for the Calin and ESSG IBP criteria. For the ESSG and Berlin 7b criteria, non-Hispanic white persons had significantly higher IBP prevalences compared with Mexican Americans. Conclusions IBP is associated with spondyloarthritis. Awareness of the prevalence of IBP may be useful for planning future epidemiological studies as well as development and validation of diagnostic and classification criteria for specific clinically defined diseases.

Introduction. Over the years, Outcome Measures in Rheumatology Clinical Trials (OMERACT) has worked toward consensus on core sets for outcome measurement in specific rheumatologic diseases. OMERACT core sets refer to the minimum number of domains and instruments essential to address the desired outcomes in trials. “Domains” are the attributes of an activity or function. This article discusses the need for an open process for selecting domains, existing frameworks for choosing domains, and the importance of describing the methods for selecting domains. Methods. We reviewed the domains selection process of 3 OMERACT groups working on patient-reported outcomes (PRO). We categorized these methods in a hierarchy of comprehensiveness and examined the extent to which they address related issues. Results. There was agreement that a gold standard for domain selection would include 3 important aspects: following a framework, remaining true to the clinical question, and including the clinically relevant outcomes for both benefits and harms. Discussion. OMERACT participants agreed that a guide for the options for developing domains that meet the OMERACT Filter would be useful. More discussion and explanation is needed to outline outcomes related to the patient perspective that are not covered by the current version of the International Classification of Functioning, Disability and Health (ICF) and to explain the usefulness of the population/intervention/comparison/outcome (PICO) structure in domain selection. Future OMERACT work includes addressing these issues and developing a framework based on the ICF to support comprehensive outcome measurements.

Objective.Traditional outcome measures in randomized controlled trials (RCT) include well-established response criteria as well as ACR EULAR responses using Disease Activity Score 44 (DAS44)/DAS28 to assess improvement; however, a measure to assess worsening of disease has yet to be developed. This special interest group (SIG) was established to develop an evidence-based, consensus-driven standard definition of “flare” in rheumatoid arthritis (RA).Methods.At OMERACT 8, the need for a standardized definition of RA flare was recognized; interested individuals developed a proposal to form a SIG. A literature review was performed to identify publications and abstracts with flare definitions applied in RA, JIA, and lupus RCT as well as concerning patient perspectives on disease worsening. A SIG was held at OMERACT 9 with breakout sessions for patients and investigators.Results.The RA flare SIG was attended by about 120 participants, including 11 patients. Patients and investigators held separate breakout sessions to discuss various aspects of disease worsening. The following consensus was obtained at OMERACT 9: a working definition of flare should indicate worsening of disease activity (88%), persistence, and duration as critical elements (77%), and consideration of change or increase in therapy (74%).Conclusion.A working definition of RA flare was developed based on these votes: flare is any worsening of disease activity that would, if persistent, in most cases lead to initiation or change of therapy; and a flare represents a cluster of symptoms of sufficient duration and intensity to require initiation, change, or increase in therapy. Using this working definition, evaluation of candidate domains will be conducted via Delphi exercise and further informed by patient focus groups. Validation of candidate definitions in appropriate RCT will be required.