TNF and ankylosing spondylitis: ASDAS-CRP: Ankylosing Spondylitis Disease Activity Score based on C-reactive protein; BASFI: Bath Ankylosing Spondylitis Functional Index; BMI: body mass index; BSADAI: Bath Ankylosing Spondylitis Disease Activity Index; SD: standard deviation; SECU: secukinumab; TNFi: tumor necrosis factor inhibitor