PDE4A and psoriatic arthritis: In the last two decades many PDE4 selective inhibitors have been studied, and some of them have been evaluated in clinical trials for several inflammatory conditions, such as IBD, asthma, Chronic Obstructive Pulmonary Disease (COPD), atopic dermatitis, multiple sclerosis, psoriasis, Psoriatic Arthritis (PsA), and rheumatoid arthritis [14].