Interrater variability limits rheumatologic opinion as a reference standard for early inflammatory arthritis (IA) classification. The study objectives were to determine whether rheumatologic opinion is associated with potential early IA classification methods despite high interrater variability, and to compare the relative strengths of those associations.
Eighteen rheumatologists independently classified 30 initial rheumatology presentation summaries as early IA or not and recommended a pharmacotherapy. Case fulfillment of the following classification methods was independently determined: early referral to rheumatology recommendation for rheumatoid arthritis (ERRR), common early IA cohort inclusion criteria (CEAC), and prevalent IA classification criteria (American College of Rheumatology [ACR]/European Spondylarthropathy Study Group [ESSG]). Associations between rheumatologic opinion, disease-modifying antirheumatic drug (DMARD) recommendation, and each classification method were determined.
Participating rheumatologists published on early IA and represented 3 continents. The median case was age 43 (interquartile range [IQR] 30-53) years, had 40 (IQR 24-104) weeks of symptoms, 60 (IQR 18-120) minutes of morning stiffness, a swollen joint count of 6 (IQR 1-13), and an erythrocyte sedimentation rate of 25 (IQR 10-51) mm/hour. The mean ± SD multiple-rater kappa for rheumatologic opinion on early IA was 0.16 ± 0.02. The common odds ratios for associations between rheumatologic opinion and ERRR, CEAC, and ACR/ESSG were 10.3 (95% confidence interval [95% CI] 4.6-23.2), 4.4 (95% CI 2.5-7.7), and 0.7 (95% CI 0.4-1.1), respectively. Odds ratios for associations between DMARD recommendation and ERRR, rheumatologic opinion, CEAC, and ACR/ESSG were 18.7 (95% CI 8.1-43.2), 10.6 (95% CI 6.0-18.8), 2.8 (95% CI 1.7-4.6), and 0.5 (95% CI 0.3-0.7), respectively.
Classification methods can be used to harmonize rheumatologic opinion of early IA despite high interrater variability. The ERRR is very strongly associated with both rheumatologic opinions of early IA and DMARD treatment recommendations.