MMP8 and psoriatic arthritis: CRP: c-reactive protein; MMP-8: matrix metalloproteinase 8; CTX-1: carboxy-terminal crosslinked telopeptide of type 1 collagen; RANKL: receptor activator of nuclear factor kappa B ligand; BMI: body mass index; DAS28CRP: disease activity score using 28 joint counts based on c-reactive protein; BSA: body surface area; DAPSA: disease activity in psoriatic arthritis