TNF and psoriatic arthritis: Anti-tumour necrosis factor (TNF)-α agents are increasingly being used for the treatment of patients affected by inflammatory bowel disease (IBD) such as ulcerative colitis (UC) and Crohn’s disease (CD), as well as rheumatologic and dermatological disorders such as rheumatoid arthritis (RA), juvenile idiopathic arthritis (JIA), ankylosing spondylitis (AS), psoriatic arthritis (PsA), and psoriasis.