Evaluation of the predictive accuracy of MRI-detected erosions in hand and foot joints in patients with undifferentiated arthritis

Radiographic erosions are a clear hallmark of rheumatoid arthritis (RA). The European League Against Rheumatism (EULAR) definition of radiographic erosive disease has a high specificity, and its fulfilment alone is sufficient to classify RA.1 However, the sensitivity of radiography to detect erosions early in the disease is low. Other imaging techniques, such as MRI, are more sensitive to detect erosions than radiography and are therefore recommended by a EULAR imaging task force.2 To determine the specificity of MRI-detected erosions, we recently compared erosions in the metacarpophalangeal (MCP) and metatarsophalangeal (MTP) joints (scored according to the RA MRI Scoring System (RAMRIS)3) of patients presenting with RA with those of symptom-free persons and patients presenting with arthritides other than RA.4 MRI-detected erosions were present in all groups; therefore, the specificity of the presence of any MRI-detected erosions was low. By evaluating different erosion features, a few features were identified as specific for RA; these were severe erosions (grade ≥2, defined as >10% of bone eroded), erosions in MTP5 and erosions in MTP1 in persons aged <40. A subsequent and clinically relevant question is whether MRI-detected erosions in patients presenting with undifferentiated arthritis (UA) are valuable in predicting future progression to RA. This was explored to a limited extent in our previous study but as the number of patients with UA was limited (n=192), the predictive value of the different ‘RA-specific …