Latent profile analysis approach to the relationship between patient and physician global assessments of rheumatoid arthritis activity

Objective Patients and physicians commonly differ in their assessments of rheumatoid arthritis (RA) activity. Clinically meaningful discordance thresholds or validation of their ability to predict functional outcomes are lacking. We explored whether an unbiased, person-centred latent profile analysis (LPA) approach could classify cases based on patient global assessment (PtGA) and physician global assessment (MDGA) assessments of RA activity. We further examined whether the LPA groups displayed greater differences in clinical outcomes compared with traditional threshold-based groups. Finally, we evaluated whether LPA yielded higher explanatory power for clinical outcomes. Methods LPA was performed in 618 patients with established RA from a single centre. A threshold-based discordance definition was used as a comparator, with patients classified into concordant (PtGA-MDGA within +/- 3 cm), positively discordant (PtGA-MDGA >= 3 cm) and negatively discordant groups (PtGA-MDGA <=-3 cm). Results LPA yielded five distinct groups: low PtGA/low MDGA (35.9%), moderate PtGA/moderate MDGA (18.6%), high PtGA/high MDGA (14.7%), high PtGA/low MDGA (23.3%) and low PtGA/high MDGA (7.4%). Groups differed across clinical, physical function, pain, fatigue, health-related quality of life, work productivity and activity impairment outcomes (p<0.001). Concordance groups, in particular, displayed marked heterogeneity in outcomes depending on the magnitude of disease activity reported, with the low/low group faring the best (p<0.001). The LPA solution demonstrated superior explanatory power for all outcomes (p<0.001). Conclusions We confirmed the validity and advantages of LPA in characterising the relationship between PtGA and MDGA over a conventional threshold-based definition. LPA yielded optimally distinct, clinically meaningful and cohesive groupings, demonstrating superior explanatory power for disease-related outcomes of interest.