IntroductionPsoriatic arthritis (PsA) is an inflammatory disease characterised by synovitis, enthesitis, dactylitis and axial involvement. The prevalence of axial involvement ranges from 25% to 70% in this patient group. Treatment recommendations for axial PsA were mainly extrapolated from guidelines for axial spondyloarthritis, and the main treatment options are non-steroidal anti-inflammatory drugs and biological disease-modifying antirheumatic drugs (tumour necrosis factor, IL-17 and IL-23 inhibitors). Tofacitinib was approved for the treatment of PsA and its efficacy on axial inflammation has been demonstrated in a phase II study of ankylosing spondylitis (AS). This prospective study aims to evaluate the efficacy of tofacitinib in reducing inflammation in the sacroiliac joints (SIJs) and spine on MRI in patients with axial disease of their PsA presenting with active axial involvement compatible with axial PsA.Methods and analysesThis is a randomised, double-blind, placebo-controlled, multicentre clinical trial in patients with axial PsA who have evidence of axial involvement, active disease as defined by a Bath AS Disease Activity Index score of ≥4 and active inflammation on MRI of the SIJs and/or spine as assessed by and independent central reader. The study includes a 6-week screening period, a 24-week treatment period, which consist of a 12-week placebo-controlled double-blind treatment period followed by a 12-week active treatment period with tofacitinib for all participants, and a safety follow-up period of 4 weeks. At baseline, 80 subjects shall be randomised (1:1) to receive either tofacitinib or matching placebo for a 12-week double-blind treatment period. At week 12, an MRI of the whole spine and SIJs will be performed to evaluate the primary study endpoint.Ethics and disseminationThe study will be performed according to the ethical principles of the Declaration of Helsinki and the German drug law. The independent ethics committees of each centre approved the ethical, scientific and medical appropriateness of the study before it was conducted.Trial registration numberNCT04062695; ClinicalTrials.gov and EudraCT No: 2018-004254-22; European Union Clinical Trials Register.