FRI0587 Low back pain due to enthesopathy of erector spine muscle: a comparative us and mri study in patients with iliac crest pain syndrome
Authors: P.T. Todorov, M. Kalcheva, A. Marinkov, A. Batalov
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Iliac crest pain syndrome (ICPS) is a regional pain syndrome, that is particularly common in patients with low back pain (LBP). It is characterised clinically by pain perceived maximally at the most medial part of the posterior iliac crest, and patients' recognition of the pain provoked by a systematic digital palpation in this area, as "their" typical one. Though ICPS is very frequently encountered in LBP, the exact etiology of this syndrome was not established. Based on anatomical data, it was suggested that ICPS could be caused by a tendopathy/enthesopathy of erector spine (ES) muscle attachments to the medial iliac crest (MIC)(.<sup>1</sup> In a previous anatomical and ultrasound (US) study we showed that this in fact might be the case. <h3>Objectives</h3> The purpose of this study was, regarding the existing clinical diagnostic criteria for the ICPS as a "gold standard", to establish the sensitivity, specificity, positive and negative predictive values (PPV and NPV) and the overall accuracy of the US and the Magnetic Resonance Imaging (MRI) assessment of the entheses of the ES muscle at the MIC in patients with LBP and features indicative of ICPS. <h3>Methods</h3> 25 patients (9 men, 16 women, mean age 43.12±11.83. mean BMI 25.07±2.36) with anamnesis of chronic "nonspecific" (after lateral X-ray and standard clinical examination) LBP perceived maximally in the region of the MIC uni- or bilaterally were included. First a systematic palpation of the posterior MIC bilaterally was performed to diagnose ICPS clinically. Then in two successive days each patient underwent MRI examination of the lower back (lumbar and sacroiliac regions), with an enlarged field of view in the sagittal plane, and a standardised US examination of the ES terminal tendons and entheses bilaterally. The MRI were assessed by a radiologist with 10 years of experience in MRI. The sonographies were performed by a rheumatologist with 7 years of experience in US and analysed in regards with the OMERACT definition of enthesopathy. As a single US lesion at any enthesis is a common finding, the presence of at least two pathological features were required to classify given entheses as abnormal. <h3>Results</h3> : ICPS was identified clinically in 20 of the patients (15 unilateral and 5 bilateral), thus 25 of the total 50 entheses were clinically pathological. Comparing to the clinical findings, the calculated sensitivity, specificity, PPV, NPV and overall accuracy of the US and the MRI assessments of the ES enthesis at the MIC are placed in table 1: <h3>Conclusions</h3> This study shows that enthesopathy of the ES muscles could be the unrecognised cause for most of the cases of ICPS –a regional syndrome particularly common in LBP. US performed better than the MRI in diagnosing this pathological condition, that may reflect the fact that radiologists are not used to assess these structures. The good diagnostic properties of US in ICPS could be of value when assessing patients with otherwise "nonspecific" LBP. <h3>Reference</h3> [1] Bogduk N. Clinical anatomy of the lumbar spine and sacrum. Elsevier2005. <h3>Disclosure of Interest</h3> None declared