IL17A and psoriatic arthritis: Psoriatic arthritis (PsA) is a specific form of peripheral SpA linked to the presence of cutaneous psoriatic disease and affects up to 30% of patients with psoriasis [4]; it is recognized as a systemic condition with a particular pathogenic chain involving immune cells implicated in the type 1 immune response, especially T helper (Th) 1 lymphocytes, Th17 and Th22, and their proinflammatory cytokine complex: tumor necrosis factor α (TNFα) and interleukins (IL–17, IL-22) [5,6].