Examination of IgM rheumatoid factor (IgM-RF) and anti-cyclic citrullinated peptide antibody (anti-CCP Ab) in Japanese patients with palindromic rheumatism.

We have studied the serology of 6 patients with palindromic rheumatism. None of the patients fulfilled the classification criteria for rheumatoid arthritis at the entry; however, 4 out of the 6 patients were seropositive for IgM rheumatoid factor (IgM-RF) at entry. Sequential serological study was performed in 4 patients; IgM-RF changed from seronegative to seropositive in one patient, and the titer increased in another patient. Anti-cyclic citrullinated peptide antibody (anti-CCP Ab) at the entry was detected in only one of the 6 patients; that patient later developed RA. Although follow-up is necessary, the present study may suggest the importance of serological examination, especially anti-CCP Ab, in patients with palindromic rheumatism.