Background/Purpose: Enthesitis is a characteristic feature of spondyloarthritis (SpA). Tenderness at enthesial points constitutes clinical enthesitis. However, this may not always correlate with actual inflammation at entheses. We assessed the agreement between enthesitis by clinical exam and whole body MRI (WB MRI).

Methods: Patients enrolled in an observational study on SpA who had undergone WB MRI and clinical exam for enthesitis were included. Patients had one of the following conditions: enthesitis related arthritis (ERA), psoriatic arthritis (PsA) (ILAR criteria); undifferentiated SpA (Amor or ESSG criteria); axial SpA (ASAS criteria); juvenile ankylosing spondylitis (AS) or adult AS (Modified NY criteria). Patients underwent detailed clinical exam including manual palpation of 34 enthesial sites by one of 2 examiners. Patients underwent WB MRI without contrast. Criterion for enthesitis by WB MRI was an increased signal on STIR sequence or presence of bony erosions or bone marrow edema at the sites of tendon attachments to bones. Four healthy volunteers also underwent clinical enthesial exam and WB MRI. Median, IQR calculations were performed for descriptive statistical analysis. Kappa statistics were used to assess agreement between enthesitis by clinical exam and WB MRI.

Results: Thirteen patients had WB MRI (66% were younger than 16 years at symptom onset; 66% male; 100% Caucasian). The median disease duration was 36 months (IQR 17.5-108). Inflammatory back pain by ESSG criteria was present in 92%; Median Schober test was 5 cm (IQR 4.15-6.25). Median ESR was 8 mm/hr (IQR 5-21.5) and CRP was 0.52 mg/L (IQR 0.16-26.72). Seventy seven percent of patients satisfied ILAR criteria for ERA (N=8) or PsA (2); 46% satisfied criteria for axial SpA (6). One patient had AS. All patients had at least one tender enthesis on exam; 77% had more than 4 tender entheses. A total of 108 enthesial sites were present among patients. The most common tender enthesial sites were medial epicondyle (N=7), L5 spinous process (6), anterior superior iliac spine (7), plantar fascia insertion to MTP (8), and 1^st costosternal junction (7). None of the patients had tender Achilles insertion. Two patients had any evidence of enthesitis by WB MRI. Greater trochanter (2) and iliac crest (1) were the most common sites of enhancement on MRI. 

There was poor agreement between WB MRI and clinical exam for enthesitis when evaluated for all enthesial sites (kappa=0).  Agreement at individual sites including Achilles insertion, plantar fascia insertion to calcaneus and MTP; greater trochanter; upper and lower poles of patella; and iliac crest was also poor (k range -0.23 to 0.24). Only one enthesial site in one patient was positive both on WB MRI and clinical exam. Among 4 healthy controls, a total of 4 enthesial sites were positive by clinical exam and none were positive by WB MRI.

Conclusion: There is poor agreement between enthesitis by clinical exam and WB MRI in young patients with SpA. Clinical examination may overestimate enthesitis, or non-contrast WB MRI may have limited sensitivity to detect enthesitis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/whole-body-magnetic-resonance-imaging-in-evaluation-of-enthesitis-in-spondyloarthropathy/