This study aims to evaluate more objectively, through an imaging technique such as ultrasound, changes in joints and entheses of patients with active psoriatic arthritis (PAs) who will start treatment with Apremilast after the failure of other therapies such as synthetic DMARD (metrotrexato , Leflunomide ...).

The hypothesis of the study is that the technique of ultrasound can demonstrate the efficacy of Apremilast in the treatment of patients with active PAs

Inclusion Criteria:

• Adults 18 years of age or older with Psoriatic Arthritis (PsA) according to Classification Criteria for Psoriatic Arthritis (CASPAR) criteria at the time of selection, with involvement of hands and/or feet with active clinical disease (more than two swollen joints)
• Present 2 or more joints with ultrasound synovitis at the screening visit
• Present 1 or more entheses affected as shown by ultrasound at the screening visit
• Accept and sign the informed consent of the study
• Ability to comply with all tests and visits of specified protocol and have a permanent address.
• Women of childbearing potential must have a negative pregnancy test at the baseline visit. Women of childbearing potential who participate in the study should use one of the following contraceptive methods throughout the trial and for at least 28 days after taking the last dose of study medication.
• Approved contraceptive options are:

Option 1: Any of the following: hormonal contraceptives (e.g., birth control pills, injection, implant, transdermal patch, vaginal ring); intrauterine device (IUD); tubal ligation; or her partner has had a vasectomy OR Option 2: Male or female condom (a latex condom or non-latex condom but NOT made of natural membrane [animal, e.g., polyurethane]) AND one of the following additional barrier methods: a) diaphragm with spermicide; B) cervical cap with spermicide; or c) contraceptive sponge with spermicide.

Exclusion Criteria:

• Concomitant treatment with methotrexate or leflunomide or other DMARDs. Patients may not have taken methotrexate during the month prior to screening, leflunomide during the 2 months prior to screening and other DMARDs during the 15 days prior to screening
• Prior or current use of biological therapy (anti-TNF)
• Failure to meet any of the inclusion requirements
• Medical contraindications for taking Apremilast
• Pregnancy or breastfeeding
• History of allergy to any component of the study drug
• Active tuberculosis (TB) or history of incomplete treatment for tuberculosis
• Substance abuse or history of substance abuse within 6 months prior to screening
• Bacterial infections requiring treatment with oral or injectable antibiotics, or significant viral or fungal infections, within 4 weeks prior to screening
• Malignancy or history of malignancy (except in situ basal or squamous cell skin carcinomas treated [i.e., cured] and treated cervical intraepithelial neoplasms [i.e., cured] or carcinoma in situ of the cervix without evidence of recurrence within the last 5 years)
• Use of systemic corticosteroids at doses >10 mg/day at the time of screening and 4 weeks before
• Use of potent cytochrome CYP3A4 enzyme inducers (e.g., rifampicin, phenobarbital, carbamazepine, phenytoin, St. John's wort and grapefruit juice) at the time of screening, 4 weeks before or during the study
• Use of phototherapy within 4 weeks prior to screening (i.e., Ultraviolet B (UVB), psoralen and ultraviolet A (PUVA))
• Use of any investigational drug within 4 weeks prior to screening
• Prior treatment with Apremilast