Background/Purpose: Identifying patients that will develop rheumatoid arthritis (RA) among those presenting with undifferentiated arthritis (UA) remains a clinical dilemma. According to EULAR recommendations magnetic resonance imaging (MRI) is helpful. An important limitation is that UA is not uniformly characterized. UA is formally defined as not fulfilling RA classification criteria (1987- or 2010-criteria). In clinical practice, rheumatologists identify UA based on clinical expertise. The diagnostic value of MRI has only been determined in UA-patients not fulfilling the 1987-criteria. The data on the value of MRI in UA according to the two common and current definitions is lacking. Therefore, we performed a large study to determine this.

Methods: In total 1234 patients, consecutively included in the Leiden early-arthritis cohort (EAC) between august-2010 and march-2020 underwent MRI-scans of hand and foot, that were scored for erosions, bone marrow edema (BME), synovitis (SYN) and tenosynovitis (TS). Two UA-populations were studied: not fulfilling 1987/2010-criteria and having no other diagnosis (criteria-based UA-population, n=405), and expert-opinion of UA (n=564). Patients were followed up for RA-development (fulfilling 1987/2010-criteria) after 1-year. Logistic regression was used, test characteristics and predictive values were determined, also in clinically-relevant subgroups.

Results: Within criteria-based UA-patients, 21% developed RA. Except for BME, all MRI-features were prognostic for RA-development. Only MRI-TS was independently associated with RA-development (OR 2.79, 95% CI: 1.40-5.58), especially within ACPA-negative UA-patients (OR 2.91; 1.42-5.96). Particularly within the oligoarthritis-subgroup, MRI-TS was predictive for RA-development (NPV 93%; PPV 28%; sensitivity 85%; specificity 45%). Compared with oligo-/polyarthritis alone, MRI-TS improved prediction of RA-development within the oligoarthritis-subgroup (Net Reclassification Index 0.28). Similar results were found in the expert opinion UA-population.

Conclusion: This large cohort study showed MRI has additional prognostic value for early identification of RA. The value was highest within ACPA-negative UA-patients with oligoarthritis. Although cost-effectiveness remains to be determined, this shows MRI is useful for early recognition of RA in subgroups of UA-patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-additional-value-of-mri-in-diagnosis-of-rheumatoid-arthritis-in-undifferentiated-arthritis-patients/