In regards to "Lower TNF Inhibitor Persistence in Spondylitis", I suspect the explanation may involve some degree of "overdiagnosis" based on history and imaging and other "ill defined" medical comorbidities associated with SpA. Even if the diagnosis of SpA is well supported, axial symptoms are common and multifactorial (FMS, DDD, DJD, etc), and may be more related to such conditions that do not respond to anti-TNF agents.