Preface
Back pain is one of the most common complaints in patients, and there is no single disease feature with sufficient sensitivity and specificity to independently diagnose axial spondylitis (axSpA), so diagnosing axSpA can be challenging and has many pitfalls. In this context, Professors Floris A. van Gaalen and Martin Rudwaleit, members of the International Spondyloarthritis Association (ASAS), share three pitfalls to avoid when diagnosing axSpA, namely using classification criteria as diagnostic criteria, diagnosis by simply counting features of spondyloarthritis, Over-reliance on imaging findings. The details are as follows.
Pitfall 1: Use classification criteria for diagnosis
Basically, as with all rheumatology and musculoskeletal diseases, the axSpA classification criteria were developed for research purposes. As a standardized definition, the primary purpose of the classification criteria is to establish well-defined, relatively homogeneous cohorts for clinical and laboratory studies. The current classification criteria for axSpA were developed by ASAS in 2009.
In the blink of an eye, the taxonomy may give you the impression that the application is simple, but it is not. The use of classification criteria for diagnosis not only ignores the important issues of differential diagnosis, but also leads to misdiagnosis and missed diagnosis in some patients. In a meta-analysis of 4990 patients from seven studies, the ASAS axSpA classification criteria had a sensitivity of 82% (95% CI 77-96%) and a specificity of 87% (95% CI 78-92%).
Pitfall 2: Simply add up the SpA features for diagnosis
In patients with chronic back pain (CBP), the presence of one or more features of SpA increases the likelihood of a diagnosis of axSpA. ASAS's modified Berlin algorithm suggests that patients with 4 features of SpA can be diagnosed with axSpA in the absence of further imaging or HLA-B27 detection. However, it is important to emphasize that the ASAS-modified Berlin algorithm is only a tool to help rheumatologists diagnose axSpA, and cannot and should not replace the differential diagnostic procedures for patients with CBP.
Because the clinical manifestations of SpA are diverse and involve multiple aspects of diseases such as genetic risk (e.g., HLA-B27), peripheral joint and axial spondyloarthritis, and extra-articular manifestations, the collected SpA features should form a meaningful assemblage and be directed to axial bone inflammation. For example, a patient with peripheral spondyloarthritis with psoriasis, arthritis, and dactylitis does not mean that axSpA was responsible for chronic back pain, even though the patient already had at least three features of SpA.
There is a concern among experts that there is a risk of over-diagnosing axSpA if it is simply counted SpA features without clinical reasoning and without attention to the differential diagnosis. The SPACE cohort study analyzed the relationship between the number of SpA features and the diagnosis of axSpA. Of the 500 patients suspected of axSpA, 250 (50%) were diagnosed with axSpA, of which 24% of the patient population with 1 SpA feature were diagnosed with axSpA, 43% of the patient population with 2 SpA features, 62% of the patient population with 3 SpA features, and 85% of the patient population with 4 SpA features were diagnosed with axSpA. This suggests that the increase in the number of SpA features does increase the likelihood of axSpA, but in rheumatology practice, multiple SpA features do not allow clinicians to automatically arrive at the diagnosis of axSpA, and clinical reasoning and differential diagnosis are still required.
Pitfall 3: Over-reliance on imaging results
Imaging studies play a very important role in diagnosing axSpA. Among them, MRI is increasingly used to examine sacroiliac joint inflammation and can reflect a variety of lesions associated with axSpA, but bone marrow edema (BME) has been considered the most useful diagnostic method. For suspicious BME lesions, structural lesions may increase confidence in the diagnosis.
It is important to note that other causes of sacroiliac (SI) joint bone marrow edema, such as mechanical stress, should always be considered. Previous literature has reported that patients and individuals with non-axSpA may also develop BME in SI joints.
- Of the 47 Dutch healthy volunteers, 23% of the participants showed "sacroiliitis positive" on MRI, 92% of 47 axSpA patients showed "sacroiliitis positive" on MRI, and 6% of 47 patients with chronic back pain showed "sacroiliitis positive" on MRI. In addition, 24 percent of 13 runners and 7 of 57 women with postpartum low back pain had positive MRIs.
- A Danish study found that 30-41% of recreational runners and ice hockey players had a BME that met the ASAS definition, with the posterior lower iliac bone being the most commonly affected joint quadrant, and these people had little to no bone erosion.
In summary, as with sacroiliitis on x-ray, BME MRI findings alone do not necessarily diagnose axSpA, and MRI findings should always be interpreted in conjunction with other clinical and laboratory findings.
参考文献：van Gaalen FA, Rudwaleit M. Challenges in the diagnosis of axial spondyloarthritis. Best Pract Res Clin Rheumatol. 2023 Sep; 37(3):101871. doi: 10.1016/j.berh.2023.101871.
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