The Role of Skeletal Radiology and the Limits of Serologic Assays in Distinguishing among the Causes of Inflammatory Arthritis

Radiologic findings are important for the diagnosis and treatment of inflammatory joint disease. Current classification criteria utilize different serological findings, such as anti-citrullinated-peptide antibodies (ACPA) and rheumatoid factor (RF), as well as clinical findings, for diagnosis of rheumatoid arthritis (RA). The presence of erosions allows diagnosis, even if serological criteria are not fulfilled. However, the pertinent erosions are not clearly defined. Previous studies have shown different patterns of radiographic changes in RA patients, possibly representing different mechanisms of damage. The association between different damage patterns and serological findings is not known. This study explores the association between serological factors and radiographic findings in patients with a clinical diagnosis of RA, RF-/ACPA-positive and negative, and spondylarthropathy, from a single centre. Anonymized radiographs were evaluated blindly, assessing presence of osteopenia, marginal and subchondral erosions, peri-erosional sclerosis, joint surface crumbling, and joint fusion. Radiological diagnosis was then correlated with serological findings. 193 patients were studied (RA/spondylarthropathy 151/42). Age and disease duration did not differ significantly between the groups. Subchondral and wrist erosions were significantly more common in clinically-diagnosed RA patients. RF, but not ACPA, was associated with metacarpal-carpal and metatarsal-tarsal erosions. Generally, no serological or clinical parameter could reliably predict radiological changes in patients with peripheral arthritis, neither those findings associated with RA, nor those rather associated with spondylarthropathy. This study suggests that serology alone is unable to predict the mode of radiological damage in patients with peripheral inflammatory joint disease. To prevent confounding, further studies into arthritis pathophysiology should therefore take both radiological and serological findings into account.