Snapshot A 32-year-old man presents to his rheumatologist for evaluation of new-onset joint pain. He reports feeling stiffness in his lower back in the morning and in the most distal joints in his left hand. He has a past medical history of psoriasis. On physical exam, he has papules and plaques along his hairline and scalp with overlying silver scales. His left middle finger has dactylitis and the distal interphalangeal joint is swollen. Laboratory evaluation shows that he is seronegative for rheumatoid factor. He is started on apremilast. Introduction Clinical definition a seronegative spondyloarthritis associated with skin psoriasis Epidemiology incidence < 1% of population 20-30% of patients with psoriasis demographics peak incidence in 30-50 years of age risk factors scalp psoriasis nail lesions in psoriasis Etiology idiopathic Pathogenesis ↑ interferon-α, IL-6, tumor necrosis factor-α, and other inflammatory markers recruit T-cells into skin and joints osteoclasts are exposed to inflammatory molecules in the psoriatic joint, triggering osteoclast activation and causing osteolysis Associated conditions skin psoriasis other HLA-B27 autoimmune diseases Presentation Symptoms asymmetric joint involvement often distal interphalangeal joint (DIP) spine can be involved joint pain joint stiffness in the morning Physical exam swelling in the affected joints in particular the hands > feet dactylitis inflammation of entire digit causing the finger to look like a sausage psoriatic lesions sharply demarcated pink plaque with silvery scale pitting nails uveitis sacroiliitis Imaging Radiographs indications to confirm diagnosis recommend views affected joints findings bone proliferation and bone resorption pencil-in-cup deformity of DIP, demonstrating erosive changes this is distinct from rheumatoid arthritis Studies Labs negative rheumatoid factor positive HLA-B27 Differential Ankylosing spondylitis Rheumatoid arthritis metacarpal phalangeal joint involvement, not DIP Treatment Conservative weight loss indications for patients who are overweight may reduce disease activity in psoriatic arthritis Medical treatment for skin psoriasis, review here nonsteroidal anti-inflammatory drugs (NSAIDs) indication first-line therapy for mild joint symptoms disease-modifying antirheumatic drugs (DMARDs) indication if patients have > 5 joints involved, radiographic damage, or elevated inflammatory markers drugs methotrexate leflunomide sulfasalazine apremilast tumor necrosis factor-α inhibitors anti-interleukin agents ustekinumab secukinumab Complications Cardiovascular disease