Background/Purpose: COVID-19 mitigation strategies have forced rheumatologists to shift from in-person clinical visits to telemedicine, limiting their ability to carry out complete joint exams needed to score disease activity and provide target based-care for RA patients. The purpose of this study was to estimate agreement between the validated Clinical Disease Activity Index (CDAI), and an alternative patient-based CDAI (PT-CDAI) scored using patient-reported joint counts.

Methods: Data were from early RA patients (sx < 1 year) enrolled in 2 North American prospective cohort studies, CATCH (Canadian early ArThritis CoHort) and CATCH-US (Consortium of early ArThritis Cohorts-USA), from  Mar 2017-Jan 2020 and Jan 2015-Feb 2020 with complete data needed to calculate the MD-CDAI and PT-CDAI including concurrently measured patient (PT) and physician (MD) assessed 28-tender and 28-swollen joints counts (28-TJC/28-SJC) using a homunculus, MD and PT global assessments (NRS 0-10) and other PROs (pain, stiffness, fatigue, function and mental health) at baseline, 6- and 12-months follow up. MD-CDAI and PT-CDAI were scored by summing (28-TJC and 28-SJC, MD and PT global assessments) though the former was scored using MD assessed joint counts and the latter with PT assessed joint counts. The established CDAI cut-off of 10 was applied to both scores to classify patients in REM/LDA vs. MDA/HDA disease states. Descriptive statistics were used to summarize and compare baseline cohort characteristics. Bland-Altman plots were used to estimate agreement between the MD-CDAI and the PT-CDAI. Cohen’s Kappa was used to estimate agreement between scores at classifying patients into controlled (REM/LDA) vs. active (MDA/ HDA) disease states. Mixed-effects linear regression was used to identify potential predictors of greater discrepancies between MD-CDAI and PT-CDAI.

Results: Baseline characteristics of 358 ERA patients enrolled in CATCH and 102 ERA patients enrolled in CATCH-US are summarized in Table 1. Mean differences in PT vs. MD assessments were lower for swollen than tender joints (Figure). Both studies showed higher agreement at lower ranges of the CDAI and more spread in scores at higher ranges of the CDAI (Figure). Agreement between MD-CDAI and PT-CDAI scores were moderate to substantial at classifying patients with controlled vs. active disease (Table 2). Predictors of greater differences in MD-CDAI vs. PT-CDAI in mixed-effects linear regression were greater tender joints and worse stiffness in CATCH and tender joints, obesity and male sex in CATCH-US.

Conclusion: The newly calculated PT-CDAI had good agreement with the MD-CDAI at identifying active vs. controlled RA disease activity. Results suggested that PT-based swollen joints were more consistent with MD assessments than PT tender joint counts. Moreover, predictors of higher discrepancies between PT-CDAI and MD-CDAI may help identify patient subsets that could benefit most from more MD guided training at joint self-assessments and/or more probing questioning during a telehealth visit to confirm active synovitis. Although there are other validated PROs to assess disease activity, none directly assess joint involvement which is critical to informing treatment decisions.

Table 1. Baseline Characteristics show more are older, have higher BMI and non-articular pain and are current smokers in Canadian Cohort; more are female, younger and recruited with lower disease activity in CATCH-US.

Table 2. Comparisons of MD vs. PT Joint Counts and CDAI Scores

Figure. Agreement between Physician and Patient Assessed 28 Swollen and Tender Joint Counts and PT-CDAI vs. MD-CDAI in 2 Early RA Cohorts

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/can-a-clinical-disease-activity-index-based-on-patient-reported-joint-counts-pt-cdai-be-used-to-inform-target-based-care-in-telemedicine-an-analysis-of-2-early-ra-cohort-studies/