Ankylosing spondylitis and psoriatic arthritis are both types of inflammatory arthritis that can affect the back, hips, and other joints. The term “arthritis” is an informal term that describes joint pain or joint disease.
There are more than 100 different types of arthritis which vary in cause, severity, and symptoms.1 Inflammatory arthritis occurs when a person’s immune system targets their own joints, causing swelling, tissue damage, and pain. A healthy immune system protects our bodies by attacking foreign invaders such as bacteria and viruses.
What is ankylosing spondylitis?
Ankylosing spondylitis is a chronic arthritis that affects mainly your spine and the hip joints that connect the backbone and the pelvis. These are called sacroiliac or SI joints. Ankylosing spondylitis is characterized by pain and stiffness in the back and hips, caused by inflammation in the affected joints. People with ankylosing spondylitis can experience limitations in their ability to move because of pain and stiffness. Over time, the vertebrae in the spine can sometimes fuse or grow together, causing additional pain and stiffness
Ankylosing spondylitis generally begins in late adolescence or early adulthood.3
What is psoriatic arthritis?
Psoriatic arthritis occurs only in people who also have a related skin condition known as psoriasis. Like inflammatory arthritis, psoriasis is also caused by an autoimmune response. It is characterized by a scaly, red, itchy, oozing rash that most frequently occurs on the elbows, knees, and scalp, but it can occur anywhere on the body.
Up to 30% of people with psoriasis also eventually develop psoriatic arthritis, an autoimmune disease, where the immune system attacks the joints. Unlike AS, which generally begins in the back and hip bones, psoriatic arthritis most frequently begins in the finger joints. However other joints such as the toes, wrists, and ankles can also be involved.4
The most common age of onset for psoriatic arthritis is between 30 and 50.4
Back involvement in psoriatic arthritis
About 20% of patients with psoriatic arthritis eventually experience pain and swelling in their spine and hip joints. This condition is known as psoriatic spondylitis. It can lead to the same kinds of symptoms that people with ankylosing spondylitis may have, including fusion of the vertebrae—the bones in the spine.4
Researchers have identified a particular gene, known as HLA-B27, which seems to be associated with multiple inflammatory diseases. These include ankylosing spondylitis, psoriatic arthritis, psoriasis, and inflammatory bowel disease. While the gene itself does not cause these diseases, its presence seems to make it more likely for people to develop them.4
HLA-B27 is a genetic risk factor for both ankylosing spondylitis and psoriatic arthritis. However, it occurs less frequently in people with spinal psoriatic arthritis than it does in people with ankylosing spondylitis. Among people with psoriatic arthritis, those who carry the HLA-B27 gene are more likely to have their symptoms progress to their back than people who do not carry the gene.4
What Is Arthritis? Arthritis Foundation. Available at: https://www.arthritis.org/about-arthritis/understanding-arthritis/what-is-arthritis.php Accessed April 16, 2019.
Most Common Symptoms. Spondylitis Association of America. Available at: https://www.spondylitis.org/Ankylosing-Spondylitis/Symptoms Accessed April 5, 2019.
Ankylosing spondylitis. Mayo Clinic. Updated March 7, 2018. Available at: https://www.mayoclinic.org/diseases-conditions/ankylosing-spondylitis/symptoms-causes/syc-20354808 Accessed April 5, 2019.
Overview of Psoriatic Arthritis. Spondylitis Association of America. Available at: https://www.spondylitis.org/Psoriatic-Arthritis Accessed April 17, 2019.
Joy Feld, Vinod Chandran, Nigil Haroon, et al. Axial disease in psoriatic arthritis and ankylosing spondylitis: a critical comparison. Nature Reviews Rheumatology. Volume 14, pages 363–371 (2018). Available at: https://www.nature.com/articles/s41584-018-0006-8#Abs3 Accessed April 17, 2019.