MRI Findings of the Sacroiliac Joints in Patients with Low Back Pain: Alternative Diagnosis to Inflammatory Sacroiliitis - PDF Document

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  1. ORIGINAL ARTICLES ???????????19???NOVEMBER2017 MRI Findings of the Sacroiliac Joints in Patients with Low Back Pain: Alternative Diagnosis to Inflammatory Sacroiliitis Iris Eshed MD1 and Merav Lidar MD2 1Department of Diagnostic Imaging and 2Rheumatology Unit, Sheba Medical Center, Tel Hashomer, affiliated with Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel S These diseases are negative for rheumatoid factor and are often associated with the carriage of human leukocyte anti- gen B27 (HLA-B27) [1]. Inflammation of the sacroiliac joints (SIJ), or sacroiliitis, is a hallmark of SpA, typically presenting with inflammatory low back pain [2]. It is the most common early clinical finding and the presumed first manifestation of the disease in the majority of SpA patients [1]. Bony changes of sacroiliitis such as erosions, sclerosis, and ankylosis can be diagnosed by conventional radiographs and computed tomography (CT) in an advanced, already established disease. However, a more sensitive diagnostic tool, such as magnetic resonance imaging (MRI) is necessary for diagnosing and evaluating inflammation in patients with early disease [3]. The main acute inflammatory findings of sacroiliitis, observed on MRI, include periarticular SIJ bone marrow edema (BME) [Figure 1] and contrast enhancement [4], which may be seen years before late structural findings are evident [5]. The beneficial effect of biological drugs such as the tumor necrosis factor-alpha receptor blocker group has further emphasized the need for early diagnosis of sacroi- liitis in SpA patients and has accelerated the use of MRI as an effective tool for early detection of sacroiliitis [3,6]. As a result, an increasing number of SIJ MRIs are performed each year on patients with suspected sacroiliitis [7]. However, one should bear in mind that non-inflammatory diseases such as spinal degenerative changes, tumors, or infections may present as inflammatory-type back pain that clinically mim- ics sacroiliitis [8]. To this end, in this article, we aimed to evaluate and characterize the non-inflammatory conditions detected on SIJ MRIs in patients with suspected inflamma- tory sacroiliitis. pondyloarthritis (SpA) is a group of inflammatory dis- eases of which ankylosing spondylitis is the prototype. ABSTRACT: Background: Magnetic resonance imaging (MRI) is the most sensitive imaging modality for the detection of sacroiliitis. Diagnosing sacroiliitis on MRI is not always straightforward and can be challenging in some cases. Objectives: To evaluate the prevalence of alternative diagnoses suggested by MRI and characterize the MR appearance of the most common ones. Methods: Consecutive MRI examinations of the sacroiliac joints (SIJ) performed between 2005 and 2012 were retrospectively eva- luated for the presence of structural and active sacroiliitis findings according to the Assessment of SpondyloArthritis International Society guidelines. Alternative diagnoses, including degenerative changes, diffuse idiopathic skeletal hyperostosis (DISH), osteitis condensans ilii (OCI), septic sacroiliitis/discitis, stress reaction and anatomic variants, were registered. Results: We evaluated 281 MRI examinations, 116 males, 165 females, average age 44±15 years. Sacroiliitis was found in 71 examinations (25%) and alternative diagnoses were suggested in 87 (31%) (OCI 8.9%, anatomic variants 5.3%, septic sacroiliitis/discitis 5.3%, degenerative findings 4.3%, DISH 1.5%, stress reaction 0.7%, tumor 0.3%). A normal examination was found in the remaining 123 examinations. Patients with alternative diagnoses were older than those with sacroiliitis (62 vs. 47 years of age, respectively, P > 0.05). Alternative diagnoses in the SIJ were significantly more common in females (66) than in males (21), P < 0.05. Conclusions: A substantial proportion of patients with sus- pected sacroiliitis had normal SIJ while the rest were more commonly diagnosed with pathologies other than inflammatory sacroiliitis. A referral by an experienced rheumatologist may improve the sensitivity and specificity of this important exami- nation. sacroiliac joints, sacroiliitis, MRI, alternative diagnosis, spondyloarthritis IMAJ 2017; 19: 666–669 KEY WORDS: PATIENTS AND METHODS All consecutive MRI examinations of the SIJ performed in our institution, a tertiary medical center, for suspected inflamma- tory sacroiliitis between 2005 and 2012 were retrospectively evaluated. This work was presented at a radiology–rheumatology meeting focusing on the contribution of imaging to the understanding of the pathogenesis and treatment decisions in musculoskeletal rheumatic diseases that took place in December 2016 at the Sheba Medical Center, Tel Hashomer, Israel 666

  2. ORIGINAL ARTICLES ???????????19???NOVEMBER2017 Figure 1.Semicoronal T2-w with fat saturation sequence of the sacroiliac joints of a30year old male with left sided sacroiliitis. Bone marrow edema and some mild cortical erosions are demo- nstrated both on the iliac and sacral sides of the left joint (arrows) Figure 2. Semicoronal T2-w with fat saturation sequences of the sacroiliac joints B A [A] a 65 year old female with degenerative changes of the sacroiliac joints, some mild iliac sided bone marrow edema with small subchondral cysts are evident on the iliac sides of both sacroiliac joints (arrows) [B] a 45 year old male with an anterior bony bridge connecting the iliac and the sacral side of the left sacroiliac joint is seen (arrow) compatible with diffuse idiopathic skeletal hyperostosis Institutional review board approval for the retrospective review of the MRI images was obtained. Informed consent was waived due to the retrospective nature of the study. Included in the study were examinations of patients 18 years of age and older who were referred due to suspected inflamma- tory sacroiliitis. Exclusions included examinations of patients younger than 18 years of age and examinations that were tech- nically inadequate. D C [C] a 36 year old female with right sided pain. Mild iliac sided subchondral sclerosis and cortical irregularity are evident on the anterior part of the right sacroiliac joint (arrow), compatible with osteitis condensans ilii [D] an 18 year old male with septic sacroiliitis. Iliac and sacral left sided bone marrow edema is evident (arrows) as well as soft tissue edema anterior and posterior to the joint and a fluid collection (arrowheads) compatible with an iliac muscle abscess MRI EXAMINATIONS All MRI examinations were conducted on a 1.5T unit (Signa HDX, GE healthcare, Milwaukee, MN, USA) with a phased-array 8-element coil. The examination was performed in the semi-cor- onal orientation (along the long axis of the sacrum and perpen- dicular to the S2 vertebral body) in T1-W (TR = 534, TE = 8.9), T2-W with fat saturation (TR = 6079, TE = 80) and T1-W with fat saturation before and after gadolinium (Gadoterate meglumine, Dotarem; Guerbet, Roissy, France) intravenous administration (TR = 130, TE = 2.9) sequences. Sagittal images of the lumbar spine in T1-W and T2-W sequences were also obtained. [E] a 34 year old male, marathon runner. Sacral sided bone marrow edema is evident with a fracture line in its center (arrow), compatible with a stress fracture. The sacroiliac joint itself is intact with no erosions or cortical irregularity E chondral fat deposition with or without minor subchondral BME [Figure 2A] ?? ??????????????????????????????????????????????? Overt, coarse bony/ossified bridges over the anterior SIJ articular margins [Figure 2B] ?? ??????????????????????????????? Localized subchondral sclero- sis of the anterior part of the joint, mainly on the iliac side. Some bony irregularity and minor BME may be present in the same location [Figure 2C] ?? ???????????????????? Unilateral SIJ BME with or without ero- sions, joint fluid with capsular distention, pronounced MRI EVALUATION The MRI examinations were reviewed by an experienced musculoskeletal radiologist. Images were assessed for the pres- ence of structural and active sacroiliitis findings befitting the Assessment of SpondyloArthritis International Society (ASAS) definition [6,9]. Alternative diagnoses were registered when a constellation of other SIJ pathologies were noted according to the following definitions: ?? ??????????????????????????Joint space narrowing, subchondral sclerosis, subchondral cysts, osteophytes and minute sub- 667

  3. ORIGINAL ARTICLES ???????????19???NOVEMBER2017 periarticular soft tissue, and muscle edema with or without periarticular collections [Figure 2D] ?? Stress reaction: Unilateral sacral sided BME usually without involvement of the subchondral bone with an apparent ver- tical fracture line within the edematous sacrum [Figure 2E] ?? Degenerative disc disease: Loss of signal and intervertebral disc space narrowing with significant disc herniation with or without adjacent BME ?? Septic discitis/osteomyelitis: Loss of intervertebral disc space with enhancement, pronounced BME, paravertebral soft tissue, and muscle edema with or without periarticular collections Table 1. Sacroiliac joints and lumbar spine alternative diagnoses to inflammatory sacroiliitis demonstrated on the MRIs of sacroiliac joints (out of a total cohort of 281 patients) Disease Sacroiliac joints: Osteitis condensans ilii Anatomic variants Septic sacroiliitis Degenerative DISH Stress reaction Space occupying lesion N % 25 15 15 12 4 2 1 8.9 5.3 5.3 4.3 1.5 0.7 0.3 Spine: Degenerative Discitis 11 2 4 0.7 Additional registered diagnoses included: ?? Anatomic variants of the SIJ potentially causing the patient’s symptomatology, including degenerative changes in acces- sory facets of the SIJ or pseudo-arthrosis of L5 vertebra hemi-sacralization ?? Space-occupying lesions Total 87 31 MRI = magnetic resonance imaging, DISH = diffuse idiopathic skeletal hyperostosis tory back pain. We showed that only a quarter of patients referred for MRI due to a clinical suspicion of inflammatory sacroiliitis indeed harbor this pathology. A third of the patients with inflammatory back pain were found to present with non- inflammatory conditions, while almost half were found to have normal SIJ on MRI. A similar study performed by Jans and colleagues [8] reported a slightly lower percentage of alternative diseases (23%) and a higher prevalence of sacroiliitis (36%) with remarkable similarity in the prevalence of normal exams (41%). The distribution of the alternative pathologies in the SIJ in Jans’ cohort was, however, quite different. While they reported spinal degenerative changes in 44.1% of the exams, we found degen- erative changes in a mere 4%. Conversely, osteitis condensans ilii was the most frequent pathology described in our patients (8.9%) whereas it was described in only 2.5% of the European cohort. One potential explanation of the different results may be the different inclusion criteria. In our study the cohort rep- resented all those suspected sacroiliitis who were referred by either rheumatologists, orthopedic surgeons, or family physi- cians. Jans’ cohort included only patients with inflammatory back pain beginning before the age of 40 who were referred by a rheumatologist. While these different inclusion criteria may explain the higher percentage of patients with sacroiliitis in Jans’ cohort, one would have expected a much higher percent- age of sacroiliitis in such a targeted cohort. The lesson learned is therefore that inflammatory back pain in itself is not a specific enough condition, even when diagnosed by an experienced rheumatologist. This conclusion concurs with Rudwaleit’s data [10] showing that the likelihood ratio of a person with inflam- matory back pain with a diagnosis of axial SpA is no more than 3.7. Diagnostic confirmation can be assured only when addi- tional clinical criteria are taken into account, such as a good response to nonsteroidal anti-inflammatory drugs, a positive family history, anterior uveitis, dactylitis, peripheral arthritis, STATISTICAL ANALYSIS Categorical variables were analyzed by chi-square test and con- tinuous variables by Student’s t-test test, as appropriate. P < 0.05 was considered significant. Statistical analysis was performed using SPSS software version 11 (SPSS Inc., Chicago, IL, USA). RESULTS A total of 283 MRI examinations of the SIJ were performed during the defined period. Two examinations of reduced qual- ity (one due to metal artefacts and the other due to multiple motion artefacts) were excluded, leaving a total of 281 examina- tions for evaluation, 116 males and 165 females. The average age was 44 ± 15 years. Inflammatory sacroiliitis was found in 71 of 281 examina- tions (25%), 44 males and 27 females. The average age was 47 years. Alternative diagnoses were suggested in 87 additional examinations (31%), 21 males and 66 females. The average age was 62 years. A normal examination with no registered pathol- ogy was found in the remaining 123 examinations (44%), 51 males and 72 females. The average age was 35 years. Alternative non-inflammatory diagnoses demonstrated on SIJ MRI and their prevalence are summarized in Table 1. Patients with alternative diagnoses were older than ones with sacroiliitis (62 vs. 47 years of age, respectively); however, this difference was not statistically different. Alternative pathol- ogies in the SIJ were significantly more common in females than in males (66 vs. 21, respectively, P < 0.05). DISCUSSION In the current study we assessed the prevalence of various pathologies in the SIJ in patients suffering from inflamma- 668

  4. ORIGINAL ARTICLES ???????????19???NOVEMBER2017 enthesitis, elevated acute phase reactants, and HLA-B27 positiv- ity. Hence, the relatively low percentage of sacroiliitis in patients who are referred to MRI only due to inflammatory back pain, regardless of age of onset, underscores that additional clinical criteria suggestive of spondyloarthropathy is warranted to conclude the diagnosis of axial SpA in this patient population. Moreover, due to the lack of specificity of MRI examinations of the SIJ, some degree of inflammatory changes in and around the SIJ may be present in non-inflammatory conditions. These inconclusive inflammatory changes in concert with inflamma- tory type back pain may lead to an erroneous diagnosis of axial SpA and the institution of inappropriate therapy. The non-specific nature of back pain is due in part to the complex neural innervation of the pelvis. Hence, pelvic and hip pain may originate from pathology in neighboring structures, such as the lumbar spine and hip [11]. This may explain the rela- tively high percentage of alternative diagnoses encountered both in the current study and in Jans’ study, highlighting the need to focus the anamnesis and physical examination on additional SpA-related features and to encourage referral by rheumatolo- gists rather than orthopedic doctors and general practitioners. The rate of degenerative changes in the spine and SIJ reported in Jans’ study (44.1%) was tenfold higher than that found in our patients. This discrepancy is explained by the fact that we defined only substantial disc herniation as a degenerative change while they included any degenerative change in this category. Finally, we found a high rate of OCI (8.9%) among our cohort suggesting that this condition may be associated with inflammatory type back pain, as has been eluded to in several previous studies [12,13], as well as that the index of suspicion of SpA among female patients with inflammatory back pain has increased. Indeed, non-radiographic axial SpA, diagnosed in the presence of sacroiliitis on MRI in the face of normal pelvic radiographs, affects males and females equally, whereas ankylosing spondylitis, which is diagnosed based on chronic changes of the SIJ, is more predominant in males. Thus, the referral of more female patients with inflammatory back pain to MRI of the SIJ reflects the paradigm shift in recent years which has enabled more and more patients to be diagnosed in their pre-radiographic stage, before chronic changes ensue. The study’s main limitation is its retrospective nature and absence of clinical information substantiating the radiographic diagnosis. mal SIJ while the rest are more commonly diagnosed with pathologies other than inflammatory sacroiliitis despite it being the original clinical suspicion. It stands to reason that referral by an experienced rheumatologist, which may supplement the anamnesis of inflammatory type back pain with SpA targeted questions, improves the sensitivity and specificity of this impor- tant examination. Correspondence Dr. I. Eshed Dept. Diagnostic Imaging, Sheba Medical Center, Tel Hashomer 5265601, Israel Phone: (972-3) 530-2498 Fax: (972-3) 530-2220 email: iriseshed@gmail.com References 1. Dougados M, Baeten D. Spondyloarthritis. Lancet 2011; 377 (9783): 2127-37. 2. Brandt J, Bollow M, Haberle J, et al. Studying patients with inflammatory back pain and arthritis of the lower limbs clinically and by magnetic resonance imaging: many, but not all patients with sacroiliitis have spondyloarthropathy. Rheumatology (Oxford) 1999; 38 (9): 831-6. 3. Hermann KG, Bollow M. Magnetic resonance imaging of sacroiliitis in patients with spondyloarthritis: correlation with anatomy and histology. Rofo 2014; 186 (3): 230-7. 4. Baraliakos X, van der Heijde D, Braun J, Landewe RB. OMERACT magnetic resonance imaging initiative on structural and inflammatory lesions in ankylosing spondylitis--report of a special interest group at OMERACT 10 on sacroiliac joint and spine lesions. J Rheumatol 2011; 38 (9): 2051-4. 5. Bredella MA, Steinbach LS, Morgan S, Ward M, Davis JC. MRI of the sacroiliac joints in patients with moderate to severe ankylosing spondylitis. AJR Am J Roentgenol 2006; 187 (6): 1420-6. 6. Rudwaleit M, Jurik AG, Hermann KG, et al. Defining active sacroiliitis on magnetic resonance imaging (MRI) for classification of axial spondyloarthritis: a consensual approach by the ASAS/OMERACT MRI group. Ann Rheum Dis 2009; 68 (10): 1520-7. 7. Abitbul V, Lidar M, Shabshin N, Flluser G, Eshed I. [Magnetic resonance imaging for the diagnosis of sacroiliitis in Israel: our experience in the last five years]. Harefuah 2011; 150 (7): 563-7, 619, 618. [Hebrew] 8. Jans L, Van Praet L, Elewaut D, et al. MRI of the SI joints commonly shows non- inflammatory disease in patients clinically suspected of sacroiliitis. Eur J Radiol 2014; 83 (1): 179-84. 9. Lambert RG, Bakker PA, van der Heijde D, et al. Defining active sacroiliitis on MRI for classification of axial spondyloarthritis: update by the ASAS MRI working group. Ann Rheum Dis 2016; 75 (11): 1958-63. 10. Rudwaleit M, Khan MA, Sieper J. The challenge of diagnosis and classification in early ankylosing spondylitis: do we need new criteria? Arthritis Rheum 2005; 52 (4):1000-8. 11. Youssef P, Loukas M, Chapman JR, Oskouian RJ, Tubbs RS. Comprehensive anatomical and immunohistochemical review of the innervation of the human spine and joints with application to an improved understanding of back pain. Childs Nerv Syst 2016; 32 (2): 243-51. 12. Cidem M, Capkin E, Karkucak M, Karaca A. Osteitis condensans ilii in differential diagnosis of patients with chronic low back pain: a review of the literature. Mod Rheumatol 2012; 22 (3): 467-9. 13. Jenks K, Meikle G, Gray A, Stebbings S. Osteitis condensans ilii: a significant association with sacroiliac joint tenderness in women. Int J Rheum Dis 2009; 12 (1): 39-43. CONCLUSIONS In conclusion, we have taken an MRI snapshot of the SIJ of all those presenting with suspected sacroiliitis. We have shown that a substantial proportion of patients turn out to have nor- “Nothing in life just happens. It is not enough to believe in something; you have to have the stamina to meet obstacles and overcome them, to struggle” Golda Meir, (1898–1978), Israeli teacher, kibbutznik, stateswoman, politician and the fourth Prime Minister of Israel 669