Undifferentiated polyarthritis: is it a hiddrn form of RA? The value of anticyclic citrullinated peptide antibodies as a diagnostic and prognostic marker for rheumatoid arthritis

ABSTRACT

The study was undertaken to assess the value of anti-cyclic citrullinated peptide antibodies [anti-CCP] in comparison to anti-perinuclear factor [APF] and IgM rheumatoid factor [IgM RF] in the early diagnosis of rheumatoid arthritis [RA] in patients with undifferentiated polyarthritis [UPA]. Serum samples of sixty patients with UPA [not fulfilling any of the ACR criteria for the diagnosis of any of the connective tissue diseases] and of other twenty age and sex matched healthy volunteers act as a control group was tested for IgM RF, APF and anti-CCP antibodies at first visit. Follow-up and reassessment of all patients was done monthly till the end of the study after one year. Measurement of APF was done by indirect immunofluorescence [IIF] and anti-CCP was done by enzyme linked immunosorbent assay [ELISA]. Forty two [70%] out of 60 UPA patients met the revised criteria of diagnosis of RA after one year of follow-up. A positive anti-CCP test was highly specific for RA [specificity 88.8%] being found in 30 [71.5%] out of 42 RA patients and its sensitivity was [71.4%]. IgM RF had the highest sensitivity [76%] and it was less specific for RA [66.6%] while the specificity and the sensitivity of APF were 77.7% and 52.38%, respectively. There was a highly significant association between anti-CCP antibodies positive RA patients and high disease activity score as well as disease severity score [p<0.001] while there was significant association between IgM RF and APF positive RA patients separately and high disease activity score [p<0.02 and 0.01, respectively] as well as disease severity score [p<0.05 and 0.01, respectively]. These results suggest that anti-CCP antibody is a highly specific serologic marker for RA and its determination is of value in the diagnosis of early cases of RA. Furthermore, anti-CCP may have prognostic significance because of their association with more severe and active form of RA