Analysis of the Pathogenesis of Itch in Response to Apremilast Therapy in Psoriasis Patients

Inclusion Criteria: 1. Subjects must be able to understand and communicate with the investigator and comply with the requirements of the study and must give written, signed and dated informed consent before any study related activity is performed. 2. Subjects must be at least 18 years of age at time of enrollment 3. Patients with chronic moderate to severe plaque type psoriasis who failed to respond to or who have a contraindication to, or are intolerant to other systemic therapy including cyclosporine, methotrexate or psoralen and ultraviolet-A light (PUVA) 4. Subjects must have a score in the numerical rating scale (NRS, see 12.4) \>5 at baseline 5. Women of childbearing potential\* and males with female partners of child bearing potential must be ready and able to use highly effective methods of birth control per ICH M3(R2) that result in a low failure rate of less than 1% per year when used consistently and correctly. * Women of childbearing potential are defined as: * Having experienced menarche and * not Postmenopausal (12 months with no menses without an alternative medical cause) and * not permanently sterilized (e.g. tubal occlusion, hysterectomy, bilateral oophorectomy or bilateral salpingectomy) Exclusion Criteria: 1. Patients with previous treatment with Apremilast 2. Patients incapable of giving full informed consent.Patients enrolled in other clinical trials 3. Allergies against Apremilast or any of the inactive ingredients: lactose monohydrate, microcrystalline cellulose, croscarmellose sodium, magnesium stearate, polyvinyl alcohol, titanium dioxide, polyethylene glycol, talc, iron oxide red, iron oxide yellow (20 and 30 mg only) and iron oxide black (30 mg only) 4. Rifampicin, Phenobarbital, Carbamazepine, Phenytoin, enzalutamid, mitotan or St John's Wort as concomitant medication 5. Patients with rare hereditary problems of galactose intolerance, lactase deficiency or glucose-galactose malabsorption 6. Allergy to local anaesthetic or latex 7. Pregnancy/Lactation 8. Patients with known HIV infection and active or uncontrolled hepatitis B or C infection 9. Patients with known disposition for excessive keloid formation or wound healing disorders 10. Patients with other forms than chronic plaque type psoriasis especially drug-induced psoriasis 11. Patients who cannot tolerate the complete dose used in this study due to medical conditions e.g. due to kidney insufficiency 12. Patients with depressive symptom in PHQ-D in visit 1 13. Concomitant medication that can cause psychiatric symptoms 14. Psychiatric disorders