Figure 5: Correlations between clinical and serological variables. (a) Negative correlation between nitric oxide (NO) levels and intima-media thickness (IMT) values in rheumatoid arthritis (RA) and psoriatic arthritis (PsA) patients. , . (b) Negative correlation between β-carotene levels and the onset of the disease (evaluated in terms of year in which the disease was diagnosed) in RA patients. , .