Imaging Biomarkers in Crohn's Associated Spondyloarthritis

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IMAGING AND CROHN'S ASSOCIATED SpA: Crohn's disease (CD) is the most common type of inflammatory bowel disease (IBD). It affects an estimated 0.7 million patients in United States and is responsible for 0.2 million hospitalizations each year.1 Although the gastrointestinal tract is the primary site ...

IMAGING AND CROHN'S ASSOCIATED SpA: Crohn's disease (CD) is the most common type of inflammatory bowel disease (IBD). It affects an estimated 0.7 million patients in United States and is responsible for 0.2 million hospitalizations each year.1 Although the gastrointestinal tract is the primary site of inflammation, inflammatory arthritis (both peripheral and axial) can affect between 12.8-23% of patients with Crohn's Disease2,3, and axial SpA alone has been reported to effect 6.7% to 18% of Crohn's patients.4 However, in 2 recent studies5,6, radiological sacroiliitis was reported to be present in 27% and 52% in IBD patients. MRI changes of inflammation precede radiological sacroiliitis by years but it is not clear when this occurs. Presence of damage on x-ray in asymptomatic patients may suggest that Crohn's associated axial SpA could be underdiagnosed. Since Crohn's associated SpA often affects younger patients, undertreatment or missed diagnoses could have a significant impact on health related quality of life (HR-QoL) and disability during prime wage earning and child rearing years.7 "Non-radiographic axial spondyloarthritis" is a term used to describe patients with symptomatic SpA who do not have findings on plain x-rays. These patients can have identical symptoms to those with radiographic evidence of cartilage loss and erosions, and anti-TNF (anti-Tumor Necrosis Factor) therapy has been shown to be effective in those with non-radiographic SpA.8 These patients are a clinically relevant subgroup, as 20% of patients with only MRI evidence of sacroiliitis will progress to non-reversible radiographic SpA over two years.9 Therefore, MRI evidence of sacroiliitis, in conjunction with inflammatory back pain is now sufficient to diagnosis SpA. In fact, MRI imaging is a standard component of current SpA diagnostic criteria, (ASAS: Assessment of SpondyloArthritis International Society),10 and MRI changes of sacroiliitis are routinely used to identify SpA patients for clinical trials.11 However, despite these new definitions there is a deficiency of published research evaluating the clinical significance of MRI findings in patients with Crohn's disease. Of all the SpA-associated diseases, Crohn's-associated SpA has a particularly high burden of extra-articular inflammation. Studies suggest only half to two thirds of patients with CT or MRI evidence of inflammation have symptoms of inflammatory back pain.1,12 This suggests that in Crohn's disease, MRI imaging biomarkers may be identifying early disease, analogous to the way that ultrasound can identify subclinical rheumatoid arthritis.13 We therefore hypothesize that in a mixed cohort of Crohn's patients with and without inflammatory back pain, MRI imaging biomarkers will correlate with measures of health status which reflect systemic inflammatory burden, (i.e. BASDAI, SF-12) independent of symptoms of inflammatory back pain. MRI IMAGING BIOMARKERS: A POTENTIAL CARDIOVASCULAR RISK FACTOR? The observed discordance between axial inflammation seen on MRI and inflammatory back pain raises a particularly intriguing clinical question: could Crohn's patients with imaging evidence of axial inflammation but without axial symptoms potentially benefit from therapy? It is very well established that in rheumatoid arthritis and psoriatic arthritis, systemic inflammation is associated with myocardial infarction, stroke and death, and that treating inflammation improves cardiovascular outcomes.14,15. Recent population based study from Europe and Canada showed increased risk of cardiovascular mortality in patients with Ankylosing Spondylitis.16,17 Despite clear evidence that cardiovascular risk is increased in SpA, how to quantify the increased risk is not straightforward. There is no consistently reliable marker of systemic inflammation in these patients; sedimentation rate (ESR) and C-reactive protein (CRP) may not always reflect ongoing inflammation, especially in patients with non-radiographic axial SpA9. Therefore, accurately measuring the inflammatory burden in Crohn's patients, regardless of musculoskeletal symptoms, is an important area for future research. Initiation of earlier targeted therapy to decrease inflammation may not only prevent incident Crohn's associated SpA, progression of prevalent SpA, with concurrent improvements in HRQoL, but may also improve cardiovascular morbidity and mortality. In addition, although sacroiliitis is the primary axial feature in SpA, there is increasing evidence that there can also be spinal involvement even in the absence of SI joint inflammation. Recent studies suggest that spinal inflammation can occur in up to one-third of nonradiographic SpA patients with <5 years of disease duration.18 This could be an important early imaging inflammatory biomarker. To our knowledge there are no published studies evaluating spinal and SI joint MRI imaging biomarkers in Crohn's associated SpA. THE MICROBIOME: A CORRELATE OF INFLAMMATION IN CROHN'S DISEASE? The etiopathogenesis of Crohn's Disease-associated SpA remains a puzzle. As with other autoimmune diseases, interplay between genetic factors such as HLA B27 (Human Leukocyte Antigen- B27) and environmental factors likely play a role. The joint symptoms of SpA are not consistently correlated with bowel disease flares.19 Intestinal microbiota plays a critical role in evolution of our entire immune system, since axenic laboratory animals (germfree animals raised in sterile environment) were noted to have partial restoration of T cell population when these animals are colonized with filamentous bacteria. A symbiotic relationship between the main bacterial phyla is necessary for proper functioning of immune system, since notable alterations in the intestinal microbiome (i.e. dysbiosis) have been suggested in various autoimmune diseases. Reduction in taxa-diversity (such as, enterobacteriaceae, Bacteroidales and Clostridiales) and expansion of certain phyla in the intestine have been recently reported in a large cohort of new onset treatment-naïve Crohn's disease (CD) patients.20 In addition, Dr. Longman's lab has shown that the expansion of immunologically relevant Enterobacteriaceae correlates with Crohn's related SpA among a mixed group of patients with Crohn's and ulcerative colitis, (in press). However, while these are exciting data, SpA cases were identified using a non-validated clinical diagnosis, without systematic rheumatology evaluation and no imaging studies. This will be first study evaluating the microbiome in a carefully phenotyped cohort of Crohn's associated SpA, who will also have detailed MRI imaging.

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