Axial disease in psoriatic arthritis and ankylosing spondylitis: a critical comparison nature.com Inflammatory back pain in psoriatic arthritis is significantly more responsive to corticosteroids compared to back pain in ankylosing spondylitis: a prospective, open-labelled, controlled pilot study arthritis-research.biomedcentral.com HLA alleles may predict development of sacroiliitis in PsA healio.com