CEL and polyarticular arthritis: The concentration of BSSL determined in serum samples from the 43 PsA patients and 28 healthy controls showed significantly increased BSSL levels from 1.7 ± 0.2 ng/mL in healthy controls, to 2.0 ± 0.2 ng/mL in PsA patients with oligoarthritis (p = 0.018), and to 2.2 ± 0.2 ng/mL in patients with polyarthritis (p = 0.005) (Fig 8A).