PsA is classified within the broader group of SpA, chronic inflammatory arthritis that occurs in some patients with psoriasis. PsA affects about 30% of individuals with psoriasis and can cause joint pain, stiffness, swelling, and damage. It involves inflammation not only in the joints but also in entheses. This inflammation can affect any joint in the body, including the fingers, toes, spine, and SI joints. Symptoms vary widely, ranging from mild to severe, and may include dactylitis (sausage-like swelling of digits), nail changes, and eye inflammation (uveitis).
PsA fits into the pSpA spectrum because it commonly causes inflammation and arthritis in peripheral joints such as those in the hands, wrists, knees, and feet, as well as enthesitis and dactylitis. However, PsA can also have axial involvement affecting the spine, blurring the lines between axial and peripheral SpA.
pSpA includes PsA as one of its key subtypes, alongside enteropathic arthritis and ReA. The classification criteria for SpA, such as those developed by the ASAS, recognize PsA as part of the pSpA group when peripheral joints and entheses are predominantly involved. PsA shares many clinical features with other pSpA conditions, including inflammation of joints, tendons, and entheses, as well as associations with psoriasis and other systemic manifestations.
REFERENCE
1. Branch NSC and O. National Institute of Arthritis and Musculoskeletal and Skin Diseases. NIAMS; 2017 [cited 2025 Sept 25]. Psoriatic Arthritis. Available from: https://www.niams.nih.gov/health- topics/psoriatic-arthritis
2. Saalfeld W, Mixon AM, Zelie J, Lydon EJ. Differentiating Psoriatic Arthritis from Osteoarthritis and Rheumatoid Arthritis: A Narrative Review and Guide for Advanced Practice Providers. Rheumatol Ther. 2021 Dec;8(4):1493-1517.
3. Enthesitis and Psoriatic Arthritis [Internet]. 2024 [cited 2025 Sept 25]. Available from: https://www.arthritis.org/health-wellness/about-arthritis/related-conditions/physical- effects/enthesitis-and-psa
4. Overview of Spondyloarthritis What You Need to Know | SPONDYLITIS.ORG [Internet]. Spondylitis Association of America – Ankylosing Spondylitis. [cited 2025 Sept 25]. Available from: https://spondylitis.org/about-spondylitis/overview-of-spondyloarthritis/
5. Akgul O, Ozgocmen S. Classification criteria for spondyloarthropathies. World J Orthop. 2011 Dec 18;2(12):107-15.