A 45-year-old male presents with a 3-month history of progressive joint pain and stiffness. He has a 10-year history of plaque psoriasis treated with topical agents. He reports morning stiffness lasting over 1 hour, pain in the distal interphalangeal (DIP) joints of both hands, and asymmetric involvement of his knees and sacroiliac region. On examination, he has dactylitis (“sausage digits”), nail pitting, and tenderness of multiple DIP joints. Radiographs show “pencil-in-cup” deformities in the DIP joints, juxta-articular new bone formation, and sacroiliitis. Laboratory studies reveal an elevated ESR and CRP, negative rheumatoid factor and anti-CCP antibodies, and positive HLA-B27. He has had only modest relief with NSAIDs monotherapy. Which of the following is the most appropriate next step in management?