Spondyloarthritis

Looking for early signs of AS: A radiologist’s view

Thursday, 5 Mar 2020


“We need to get better at looking for those needles in the haystack. Chances are at the moment, there are more cases of nr-axSpA than we are picking up, and we can’t stop until we’ve done all we can to get patients access to the care they need as early as possible,” explains Dr Nivene Saad, Consultant Radiologist at the Princess Alexandria Hospital in Queensland. In the second of our series on non-radiographic axial spondyloarthritis (nr-axSpA), the limbic spoke with Dr Saad about the evolution of the radiologist’s role in discovering nr-axSpA and the revolution in management that ensued.

“Chronic back pain is one of the most common complaints in Australia and across the developed world.1 We always knew that a proportion of these were due to ankylosing spondylitis (AS) that exhibits irreversible structural damage visible via X-ray.2 However, years before a radiographic diagnosis could be made, patients continued to suffer debilitating pain that interfered significantly with their quality of life,”2 explains Dr Saad. “With no specific treatments available without radiographic evidence, there was nothing to offer patients except a watch and wait approach.”3

Flash back to 20 years ago with the introduction of magnetic resonance imaging (MRI), things started going in the right direction.4,5 Detection of early sacroiliitis (before radiographic structural damage ensued) became a possibility, sparking an interest in understanding a previously hidden part of the disease and potentially identifying a ‘window of opportunity’ in this condition that might modify the long-term outcome.5

When lowering the bar is better

“There’s not many times you want to lower the bar in medicine, but when MRI opened up an opportunity to recognise inflammation in patients with other hallmarks of AS, it really was an advancement,”4 notes Dr Saad. In 2009, the Assessment of SpondyloArthritis International Society (ASAS) added sacroiliitis as detected by MRI to the imaging arm of the diagnostic criteria for nr-axSpA in patients who have chronic inflammatory back pain associated with HLA B27 antigen.[Lukas] “MRI .4,5 “has been able to pick up what conventional radiography and other imaging modalities have not – that is active inflammatory changes. While other imaging techniques can identify some changes, so far MRI has the best specificity and sensitivity,”4 adds Dr Saad.

Imaging techniques for use in axial spondyloarthritis (adapted from Knmelinski)4

Technique Inflammatory/acute changes Structural/chronic changes
Conventional radiography +
CT ++
Spectral CT + ++
Ultrasound + (+)
Scintigraphy +
MRI T1w

MRI STIR/T2FS/T1Gd

(+)

++

+

+

Positron emission tomography (CT or MRI) + +

–, no diagnostic value; +, with diagnostic value; (+), limited diagnostic value; ++, with diagnostic value, gold standard. CT, computed tomography; MRI, magnetic resonance imaging; PET, positron emission tomography; STIR, short tau inversion recovery sequence; T1Gd, gadolinium-enhanced T1-weighted sequence; T1w, T1-weighted sequence; T2FS, fat-saturated T2-weighted sequence.

Characteristic lesions of the sacroiliac joints and spine that can be assessed by MRI (adapted from Knmelinski)4

Inflammatory changes Structural changes
Sacroiliac joints
Bone marrow oedema/osteitis (Sacroiliitis)

Synovitis

Capsulitis

Enthesitis

Subchondral sclerosis

Erosions

Backfill/subchondral fat metaplasia

Bony bridges

Ankylosis

Spine
Bone marrow oedema/osteitis (corner lesions)

Spondylodiscitis

Arthritis

Enthesitis of ligaments

Fat metaplasia

Erosions

Syndesmophytes

Sclerosis

Ankylosis

Inflammation detected using MRI correlates with histological and clinical findings in axSpA.4 “This, together with the fact that there is no radiation exposure with MRI compared to conventional radiography or CT, makes MRI safer for the younger patient populations where repeated imaging could be frequently required for follow-up,”4 suggests Dr Saad. “It means that when the clinical features of axSpA are there, but we cannot yet see structural damage on conventional radiography, MRI is the next option.” [Khmelinshi]4

To spot the difference, you have to know what you’re looking for

“This might seem like an obvious part of a radiologist’s role, but thinking about who the nr-axSpA patient is, puts a different perspective on this statement. While we are experts at spotting the difference, we are often guided by what to look for. I’ve seen many cases where X-ray or CT imaging performed in the ER for an unrelated issue has incidentally detected structural damage indicating AS. Considering each radiologist will probably see at least one patient a week referred from a GP or physiotherapist with non-specific back pain – that’s quite a high patient load, notwithstanding those incidental cases as well. Therefore, we need to be tuned to look for the subtle signs of nr-axSpA and make sure that the non specific finding of bone marrow oedema is thoroughly analysed to avoid false positive scan results” Dr Saad describes.

The key features radiologists look out for when it comes to nr-axSpA as defined by ASAS are:4

  • Active inflammation of subchondral or periarticular bone marrow
  • Active inflammation is defined as bone marrow edema on short tau inversion recovery sequences (STIR) or osteitis on gadolinium-enhanced T1-weighted sequences*
  • Two or more lesions must be present on the same coronal slice or a single lesion must be visible on two consecutive slices
  • Other inflammatory features of axial spondyloarthritis, such as synovitis, enthesitis, and capsulitis are uncommon in the absence of bone marrow edema and, in isolation, are not sufficient for diagnosis.

* Intravenous gadolinium contrast is not needed to diagnose bone marrow oedema hence not currently included in the MRI imaging protocol for spondyloarthritis.

“The point I emphasise to my trainees is that if we get this wrong, everything else falls out of place. Getting a patient referred for imaging is the first hurdle – so we want to make sure we don’t send them away with the wrong diagnosis as this means patients may have lost their window of opportunity to access treatment before the irreversible structural damage takes place. It’s a huge responsibility – the quality of patient lives are in our hands,” emphasises Dr Saad. She continues, “Given we are looking for that needle in a haystack, we need to be proactive in developing and honing our skills in this area, sharing our skills and cases so that in the near future, missed cases of nr-axSpA become the exception rather than the rule.

 

This article was sponsored by Janssen, which has no control over editorial content. The content is entirely independent and based on published studies and experts’ opinions, the views expressed are not necessarily those of Janssen.

 

References:

  1. Australian Government. Australian Institute of Health and Welfare. Back problems snapshot. Available at: https://www.aihw.gov.au/reports/chronic-musculoskeletal-conditions/back-problems/contents/what-are-back-problems (accessed 14 February 2019).
  2. Baraliakos X, et al. RMD Open 2015;1(Suppl 1):e000053.
  3. Brown M, Bradbury LA. Med J Aust 2017;206(5):192-194e1.
  4. Khmelinskii N, et al. Front Med 2018;5(106):1-4.
  5. Lukas C, et al. RMD Open 2018;4:e000586.

 

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