This study aims to identify and describe the presence of itch active molecules in psoriasis and response to treatment with apremilast. This data will be complemented by immunohistochemical data determining nerve ending density and neuropeptide concentrations before and during treatment and correlated with patient reported outcome. It is important to underscore that itch may interfere with various aspects of patient functioning, emotions and social status and should therefore be adequately addressed while treating patients with psoriasis