To evaluate the relationship between rheumatoid factor isotypes and articular damage detected by magnetic resonance imaging and plain radiography in early rheumatoid arthritis.
20 consecutive patients with early active rheumatoid arthritis underwent determinations of serum IgM, IgA, and IgG rheumatoid factors by enzyme-linked immunosorbent assay (ELISA). Plain radiographs of the hands and wrists were obtained, and the wrist, metacarpophalangeal joints, and proximal interphalangeal (PIP) joints on the more severely affected side were investigated by magnetic resonance imaging before and after gadolinium-DTPA injection.
IgM, IgA, and IgG rheumatoid factors were found in 13 (65%), 13 (65%), and 15 (75%) of patients, respectively. Sera from five patients (25%) contained no detectable rheumatoid factor isotypes. Correlations were found among the levels of the three rheumatoid factor isotypes. Levels of IgA, IgG, and IgM rheumatoid factor were significantly higher in patients with than without erosions on magnetic resonance imaging scans. No such difference was found when patients with and without erosions on plain radiographs were compared. Magnetic resonance imaging detected soft tissue lesions more frequently than plain radiography. Magnetic resonance imaging was also more likely than plain radiography to show bone erosions and bone cysts, but this difference was not statistically significant.
Quantitative rheumatoid factor isotype assays and magnetic resonance imaging evaluation of erosions of the hand and wrist may be useful for investigating patients with early rheumatoid arthritis.