Background Anticitrullinated peptide antibodies (ACPA) and acute phase reactants may be increased before arthritis becomes clinically detectable, suggesting that the processes underlying rheumatoid arthritis (RA) start preclinically. Whether local inflammation occurs in the preclinical phase is unknown. Therefore, we studied the small joints of ACPA positive arthralgia patients for local subclinical inflammation.

Methods Imaging was performed using 1.5 T extremity MRI. Painful hand or foot joints of 21 ACPA positive arthralgia patients without clinical arthritis were imaged. For comparison, hand and foot joints of 22 ACPA positive RA patients and 19 symptom free controls were studied. Within ACPA positive arthralgia patients, painful and symptom free joint regions were imaged. Scoring was performed according to the Outcome Measures in Rheumatology Clinical Trials (OMERACT) Rheumatoid Arthritis Magnetic Resonance Imaging Scoring (RAMRIS) method. Analyses were performed on joint region level and focused on inflammation (synovitis plus bone marrow oedema).

Results The mean combined inflammation scores of the metacarpophalangeal/proximal interphalangeal joints of controls, painful joints of ACPA positive arthralgia patients and ACPA positive RA patients were 0.1, 0.7 and 3.7, respectively (p<0.001). Likewise, the mean combined inflammation scores of the wrist were 0.9, 2.3 and 10.3, respectively (p<0.001) and that of the metatarsophalangeal joints 0.5, 0.9 and 3.8, respectively (p=0.10). At the MCP joints, the combined inflammation score was significantly correlated with C reactive protein and erythrocyte sedimentation rate levels (r_s=0.83 and r_s=0.78, respectively)

Conclusions The present data suggest that local subclinical inflammation occurs in ACPA positive arthralgia patients.