Whole-body Magnetic Resonance Imaging vs. Clinical Evaluation of Enthesitis in Patients with Spondyloarthritis

Enthesitis, the inflammation of the entheses where ligaments or tendons attach to bone, is a hallmark feature of spondyloarthritis (SpA). It often precedes joint symptoms and is associated with more severe erosive disease. Enthesitis is a key diagnostic criterion that differentiates SpA from other rheumatic conditions such as rheumatoid arthritis. Despite its clinical significance, evaluating enthesitis remains challenging due to the large number of entheses in the human body and the limitations of traditional diagnostic methods. This study explores the utility of whole-body magnetic resonance imaging (WB-MRI) in detecting and characterizing enthesitis in patients with SpA, comparing its findings with clinical evaluation methods.

Background and Significance

Enthesitis is a critical feature of SpA, particularly in its early stages. Traditional methods for evaluating enthesitis include clinical tenderness assessment, conventional radiography, ultrasonography, and conventional MRI. However, these methods are limited to localized evaluations and cannot provide a comprehensive assessment of enthesitis across the entire body. WB-MRI, a novel imaging technique, allows for the visualization of the entire body in a single examination. Although WB-MRI has lower resolution compared to conventional MRI, it offers the advantage of detecting enthesitis in multiple regions simultaneously, making it a promising tool for assessing SpA.

Previous studies have primarily focused on the application of WB-MRI in psoriatic arthritis (PsA), leaving a gap in real-world data for its use in SpA. This study aims to address this gap by investigating the distribution pattern of enthesitis in SpA patients using WB-MRI and comparing its findings with clinical evaluation methods.

Study Design and Methodology

The study was conducted at Tianjin First Central Hospital and approved by its Ethics Committee. A total of 50 patients who met the Assessment of Spondyloarthritis International Society (ASAS) classification criteria for axial SpA (ax-SpA) were initially included. After applying exclusion criteria, 30 patients were included in the final analysis. Exclusion criteria included serious primary diseases, professional athletes or fitness practitioners, a history of fractures or joint surgeries, recent glucocorticoid use, and contraindications for MRI.

All patients underwent WB-MRI using a Philips 3T Ingenia unit with phased-array coils. The MRI protocol included T1-weighted and short tau inversion recovery (STIR) sequences. Enthesitis was diagnosed based on the presence of high signal intensity on STIR images, indicating bone marrow edema (BME) or soft tissue edema, with corresponding signal loss on T1-weighted images. The evaluated entheseal sites were divided into five regions: shoulder, anterior chest wall, pelvis, knee, and foot. A total of 36 entheseal points were assessed per patient, resulting in 1080 points evaluated across all participants.

Clinical evaluation of enthesitis was performed using the modified Maastricht Ankylosing Spondylitis Enthesitis Score (MASES) and the Leeds Enthesitis Index (LEI). The clinical enthesitis score was calculated as the sum of MASES and LEI scores. The lateral epicondyle of the humerus was excluded from the clinical evaluation due to its exclusion from the MRI scanning protocol.

Results

Demographic and Clinical Characteristics

The study population had a median age of 34.9 years, with 64.5% being male. Human leukocyte antigen B27 (HLA-B27) positivity was observed in 63.3% of patients. Among the 30 patients, 20 were treated with biological agents, eight with nonsteroidal anti-inflammatory drugs (NSAIDs), and two had not received any treatment.

Clinical and WB-MRI Findings

Clinical evaluation identified enthesitis in 12% of the 450 assessed entheseal sites. The anterior chest wall was the most commonly affected region, accounting for 44% of clinical enthesitis cases. The mean clinical enthesitis score was 1.9 ± 2.4 out of a possible 15 points.

WB-MRI detected enthesitis in 9% of the 1020 evaluated entheseal sites. The pelvis was the most frequently affected region, with 28% of enthesitis cases, followed by the anterior chest wall, shoulder, knee, and foot. Specific entheseal sites with the highest frequency of enthesitis included the ischial tuberosity (10 cases), greater femoral trochanter (9 cases), and sternoclavicular joints (SClJs). The Achilles tendon and plantar aponeurosis in the foot had the lowest frequency of enthesitis.

Comparison of Clinical and WB-MRI Findings

WB-MRI identified enthesitis in 76% of patients (22 out of 30), while clinical evaluation detected enthesitis in only 57% of patients (17 out of 30). The pelvic region was the most frequently affected area in WB-MRI, with 50% of patients showing enthesitis, compared to 20% in clinical evaluation. The anterior chest wall was affected in 40% of patients in clinical assessment, while WB-MRI detected enthesitis in this region in 33% of patients.

A significant correlation was observed between WB-MRI and clinical enthesitis scores (Spearman’s rho = 0.45, P < 0.05). However, no correlation was found between WB-MRI enthesitis scores and the Ankylosing Spondylitis Disease Activity Score (ASDAS). Patients with a disease duration of more than five years had higher enthesitis scores (4.17 ± 3.24), although this difference was not statistically significant.

Intrareader Reliability

The intrareader intraclass correlation coefficient (ICC) for WB-MRI enthesitis scores was 0.91, indicating high reproducibility. This reliability was achieved through rigorous training of the radiologists using the Outcome Measures in Rheumatology Clinical Trials scoring system.

Discussion

This study highlights the utility of WB-MRI in detecting enthesitis in patients with SpA, particularly in regions that are difficult to assess clinically. The findings suggest that WB-MRI can identify subclinical enthesitis, which may not be detected through clinical evaluation. The anterior chest wall and pelvis were the most commonly affected regions, with the SClJs showing the highest proportion of enthesitis. The lower frequency of enthesitis in the lower extremities, particularly the foot, may reflect differences in mechanical stress or disease progression.

The discrepancy between clinical and WB-MRI findings can be attributed to several factors. Subclinical inflammation, which is detectable by MRI but not by clinical examination, may explain the higher detection rate of enthesitis by WB-MRI. Additionally, deep entheseal sites, such as those in the pelvis, may not be accessible to clinical evaluation through tenderness. The lack of correlation between WB-MRI enthesitis scores and ASDAS scores suggests that ASDAS may not fully capture the burden of enthesitis in SpA patients.

The high intrareader reliability of WB-MRI assessments underscores the potential of this technique for standardized evaluation of enthesitis. However, limitations such as the nonspecific nature of T2-weighted signals and the lower spatial resolution of WB-MRI compared to conventional MRI need to be addressed. Future improvements in scanning strategies and image quality may enhance the diagnostic accuracy of WB-MRI.

Conclusion

This study demonstrates that WB-MRI is a valuable tool for the comprehensive assessment of enthesitis in patients with SpA. It provides a one-stop evaluation of peripheral enthesitis, offering insights into the distribution and burden of inflammation that may not be captured by clinical methods. WB-MRI has the potential to become a standard tool for assessing disease activity and structural damage in SpA and PsA, guiding treatment strategies and improving patient outcomes.

doi.org/10.1097/CM9.0000000000001813

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