Psoriatic Spondylitis & Ankylosing Spondylitis: Differences & Similarities

Psoriatic arthritis (PsA) is an extension of psoriasis in that in addition to the presence of a scaly rash occurring primarily on the elbows, knees, and scalp (psoriasis), patients also experience chronic inflammation of the joints—usually the joints at the ends of the fingers.

Swelling and pain can also occur in other joints, like the wrists, knees, and ankles—often even the fingernails and toenails.¹

What is psoriatic spondylitis?

About one out of five patients (20%) with PsA will develop inflammation in the spine, which is known as spondylitis. This condition is called psoriatic spondylitis (PsSpA).¹

Patients with PsSpA may experience pain and inflammation along with specific or all areas of the spine, such as the neck, lower back, or pelvis. PsSpA can eventually lead to the total fusion of the spine, which happens when the spinal bones known as vertebrae become so stiff that they actually grow together, or “fuse.”^1,2

What is ankylosing spondylitis?

Ankylosing spondylitis (AS) is a very similar disease to PsSpA. Patients with AS experience inflammation, pain, and stiffness that primarily affects the spine, although other joints can become involved, such as the shoulders, hips, ribs, or heels.

As with PsSpA, inflammation of the spine can cause the vertebrae to fuse together. The hallmark feature of ankylosing spondylitis is the involvement of the sacroiliac (SI) joints during the progression of the disease. The SI joints are located at the base of the spine, where the spine joins the pelvis.^3,4 Unlike with PsSpA, however, psoriasis does not occur in AS.⁵

Is there a connection between PsSpA and AS?

PsSpA and AS are considered genetically and clinically related because both are inflammatory rheumatic diseases linked to the HLA-B27 gene. HLA-B27 is a powerful gene that increases the risk for several rheumatic diseases. The gene itself does not cause disease, but can make people more susceptible.¹

While a number of genes are linked to PsA, the highest predictive value is noted with HLA-B27. Patients who are HLA-B27 positive are more likely than others to have their disease progress to the spine and develop PsSpa.¹