Spondyloarthritis (SpA) is a group of interrelated diseases that include ankylosing spondylitis (AS), psoriatic arthritis (PsA), reactive arthritis, undifferentiated SpA, etc. About 5% to 30% of patients with axial SpA who are negative for imaging develop AS within 2 to 30 years. Inflammatory spondylitis, called axial PsA, occurs in 25% to 70% of patients with PsA and is more common in patients with a longer course of disease. In one cohort study, no axial involvement was observed in approximately 15% of patients with PsA at up to 10 years of follow-up.
The lack of a gold standard for defining axial PsA (including imaging or serum biomarkers) has hindered the progression of axial PsA. In addition, axial PsA and AS have similar clinical manifestations and genetic features, which are sometimes difficult to distinguish, which may delay the treatment of patients. Here, we have compiled the relevant literature on the identification of axial PsA and AS, hoping to bring help to your clinical work.
| Differences | Homologous | ||
| AS | Bottom bracket type PsA | ||
| genetics | % of patients with HLA-B27 presence >90%; CROSS-B*13:02,CROSS-B*40:01,CROSS-B*40:02,02,47:01,CROSS-B*51:01; 1L-23-IL-17; | HLA-B27 is present in 30-40% of patients; HLA-B*39,HLA-B*27,HLA-B*08,HLA-B*38,HLA-Cw*07:02； IL-13; | Both were HLA-B*27 positive; |
| pathology (Figure 1) | HLA-B27+状态与弥漫性脊柱骨炎相关; Critical inflammation occurs in the red bone marrow; | osteitis is lacking; Soft-tissue-centric, similar to PsA's involvement of peripheral bones, i.e., "synovial-periosteal complex soft tissues" is the target of inflammatory attack; | / |
| immunology | Osteitis occurs at the point of enthesis, which is a normal site of hematopoiesis with a rich bone marrow lineage, including neutrophil and macrophage lineage cells; | The ligament tissue is mainly composed of extracellular matrix, most of the cells are fibroblast cell lines, but there are also myeloid and lymphoid cells, and there are relatively few immune cells; | / |
| age | Teenagers, early 20s; | older age (30-40 years or older), usually presenting ≥ 10 years after the onset of psoriasis; | / |
| Site of onset | sacroiliitis; The juvenile form can begin in the mid-foot, ankle, and lower extremity joints and progress to the hip and sacroiliac joints; | neck, right thoracic vertebrae; | / |
| Clinical presentation | Almost 100% of patients present with back pain; Male multiface; Spinal mobility limitation is more pronounced; Not associated with nail lesions; | 45% of patients have back pain or may be asymptomatic; asymmetric sacroiliitis; Peripheral arthritis is more severe; Nail lesions are associated with the risk of PsA and axial PsA. | Flaming back pain; |
| Radiology | Sacroiliitis is symmetrical, and may present with bamboo changes in the late stages; | Ligamentous osteophytes are larger and more common unilaterally; Axial PsA does not fully follow the development of the anterior longitudinal ligament and does not appear on the continuous vertebrae; | HLA-B27+患者放射学损伤较高； |
| MRI | The earliest pathologies appear in the bone tissue around the fibrocartilage of sacroiliitis, manifesting on MRI as bone edema (detected using fat suppression MRI); histologic osteitis; | The location is different, osteitis is deficient; Ligaments and soft tissue disease predominantly, usually not visible on MRI, but may eventually manifest as soft-tissue-centered ossification that is different from AS; | / |
| treat | 强推荐:非甾体抗炎药、物理治疗、镇痛、TNFi、IL-17i和JAKi; 证据不足:IL-12/23i, IL-23i; | 非甾体抗炎药、物理治疗、镇痛、TNFi、IL-17i、JAKi,司库奇尤单抗,古塞奇单抗; | BASDAI can be used to assess disease activity; 不推荐:csDMARDs |
Notes: AS, ankylosing spondylitis, PsA, psoriatic arthritis, BASDAI, ankylosing spondylitis disease activity index, csDMARDs, traditional synthetic disease-modifying antirheumatic drugs, TNFi, tumor necrosis factor inhibitors, IL-17i, interleukin-17 inhibitors, JAKi, JAK inhibitors, HLA, human leukocyte antigens, MRI, MRI
Fig.1 Pathological manifestations of AS and axial PsA
参考文献：1. McGonagle D, David P, Macleod T, Watad A. Predominant ligament-centric soft-tissue involvement differentiates axial psoriatic arthritis from ankylosing spondylitis. Nat Rev Rheumatol. 2023 Dec; 19(12):818-827. doi: 10.1038/s41584-023-01038-9.2. Wang W, Lee YH, Wei JC, Mease P. Similarities and differences between axial spondyloarthritis and axial psoriatic arthritis. Int J Rheum Dis. 2023 Mar; 26(3):407-409. doi: 10.1111/1756-185X.14537.
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