Prospective open label non-randomized study, using Apremilast according to the manufacturer's Summary of Product Characteristics for 52 weeks, in patients with moderate to severe plaque psoriasis and nail psoriasis The study will be carried out in two hospital centers with experience in the management of patients with psoriasis and in the use of ultrasound of the nail apparatus. Visits and ultrasound would be performed by prescribing doctors themselves in their outpatient offices. Prior to the start of the study, the two doctors of each center will conduct a study to see the intraobserver and interobserver agreement on the ecographic parameters. The medication would be dispensed and controlled in the centers themselves and self-administered by patients at home. Each visit includes a ultrasound assessment of a target nail and measures of different scales: NAPSI, NAPPA.

Primary objective:

- Determine the percentage of patients with at least a 20% improvement over the baseline visit of the NAPPA-PBI scale in weeks 4, 16, 24, 38 and 52.

Secondary objectives:

• Determine the percentage of improvement with respect to the baseline visit of the NAPPA QoL and CLIN scale in weeks 4, 16, 24, 38 and 52
• Determine the percentage of patients, regarding baseline visit, who reach a NAPSI 50 and changes in the NAPSI scale, in weeks 4, 16, 24, 38 and 52
• Determine the percentage of improvement or change of the nail ultrasound variables with respect to the baseline visit in weeks 4, 16, 24, 38 and 52
• Explore the possible correlation between clinical (NAPSI / NAPPA-Clin) and ultrasound variables before and after treatment
• Determine the percentage of patients with sonographic signs of enthesopathy of the distal interphalangeal joint before and after treatment
• Determine differences in clinical and sonographic parameters before treatment in good responders (NAPSI 50) compared to non-responders

Inclusion Criteria:

• Patients older than 18 years old at the time of signing the IC
• Patients with the diagnosis of plaque psoriasis, moderate to severe, at least 6 months before recruitment, with nail involvement and without active psoriatic arthropathy
• Nail involvement with a minimum NAPSI of 12 for fingernails, and any NAPSI for toenails
• Patients naïve to biological treatments
• In pregnant women, pregnancy must be ruled out before treatment can be started and they must use an effective contraceptive method to prevent pregnancy during treatment

Exclusion Criteria:

• Other major or clinically uncontrolled diseases
• Pregnancy or breastfeeding
• History of allergy to any component of the study medication
• Positivity for HBV surface antigen at the screening visit
• Positivity for HCV serology at the screening visit
• Active tuberculosis or inadequately treated history of tuberculosis
• Significant abnormalities in electrocardiogram at the screening visit
• Clinically significant abnormalities of the X-ray chest at the screening visit
• History of HIV infection or other acquired or congenital immunodeficiencies
• Active abuse or history of substance abuse 6 months prior to the screening visit
• Bacterial infection that required oral or injectable antibiotics or important viral or fungal infections within 4 weeks prior to the screening visit
• Malignancy or history of malignancy (other than cured in situ cutaneous squamous cell carcinoma or basal cell carcinoma, or in situ cérvix carcinoma without evidence of recurrence in the last 5 years)
• Rebound or relapse of psoriasis in the 4 weeks prior to the screening visit
• Presence of other cutaneous diseases that could interfere in the clinical assessment of the study
• Use of topical treatments that include corticosteroids, salicylic acid, urea> 10% or calcipotriol in the 2 weeks prior to the screening visit
• Use of systemic treatments for psoriasis, including systemic corticosteroids and PUVA or UVB phototherapy, within 4 weeks prior to the screening visit
• Previous or current use of biological treatments
• Use of any investigational drug within 4 weeks prior to the screening visit
• Previous treatment with apremilast

Adults with moderate to severe psoriasis vulgaris and nail involvement and are candidates for treatment with apremilast according to the product's summary of characteristics Moderate-severe psoriasis will be considered according to the consensus document of the Spanish group of psoriasis from the Spanish Academy of Dermatology and Venereology (AEDV, 2009)