Spine School: Axial Manifestations of Psoriatic Arthritis

EULAR 2022 (VIRTUAL)—Psoriatic arthritis (PsA) is known for its ability to affect patients in many domains and manifest with enthesitis, uveitis, dactylitis and peripheral synovitis. At the 2022 Congress of the European Alliance of Associations for Rheumatology (EULAR), Philip Helliwell, MA, PhD, DM, FRCP, professor of clinical rheumatology at the University of Leeds and honorary consultant rheumatologist for the Bradford Hospitals NHS Trust, Leeds, England, discussed the importance of recognizing the axial manifestations of this disease and treating these symptoms.

In the original classification of Moll and Wright, the spondyloarthritides included such conditions as ankylosing spondylitis, PsA, reactive arthritis, Behçet’s disease, arthritis associated with inflammatory bowel disease (IBD) and Whipple’s disease.¹ These conditions shared many features, including sacroiliitis, asymmetric large joint arthritis, inflammation of the bowel, iritis, mucocutaneous ulcerations and erythema nodosum.

A number of years later, Dr. Helliwell, along with Dr. Wright, published a new classification set that eliminated Behçet’s disease and Whipple’s disease as part of this cadre and added unclassified spondyloarthritis.² These concepts of disease continue to evolve, and the distinctions between diseases have been refined, helping clinicians separate patients into more specific subtypes.

Dr. Helliwell

Radiographic Features

Dr. Helliwell went on to describe work he published in the 1990s on the differing radiographic features of axial disease seen in various forms of spondyloarthritis. Whereas the sacroiliitis of ankylosing spondylitis and IBD was noted to typically be severe and symmetrical, conditions like PsA and reactive arthritis were found to often be associated with unilateral or bilateral asymmetrical sacroiliitis. Comparing ankylosing spondylitis and IBD with PsA and reactive arthritis, the former were more frequently associated with symphysis, osteoporosis, lumbar straightening, apophyseal joint involvement, bridging syndesmophytes and ligamentous ossification.³

Not only do radiographic differences exist between PsA and other conditions with axial disease, but in PsA the clinical presentation of axial disease less often includes classical features of inflammatory back pain.

Dr. Helliwell explained that inflammatory back pain includes pain in the hips or buttocks that improves with activity and worsens with rest, occurs at night, is responsive to non-steroidal anti-inflammatory drugs and involves at least 30 minutes of morning stiffness.

A study by Feld et al. notes that axial involvement in PsA can often be asymptomatic, with only about 45% of patients with PsA and axial disease in this study reporting inflammatory back pain symptoms.⁴

Genetics & Phenotypes

Dr. Helliwell also described the interesting genetics of PsA. The HLA-C:06:02 allele is associated with the highest genetic risk of psoriasis, compared with the HLA-B27, HLA-C12–HLA-B38, and HLA-C06–HLA-B57 haplotypes, which are also associated with PsA. Interestingly, the prevalence of HLA-B27 in PsA is much lower than that seen in ankylosing spondylitis, with prevalence of 20% vs. 80%, respectively.