The term spondyloarthritis is used for a family of disorders,
such as ankylosing spondylitis (AS),
axial non-radiographic spondyloarthritis (nr-axSpA),
forms of arthritis associated with psoriasis and inflammatory bowel diseases and other conditions.
Spondyloarthritis is classified as axial or peripheral,
depending on whether patients suffer mainly symptoms in the spine,
sacroiliac joints,
hips and rib cage (the axial skeleton),
as seen in patients with ankylosing spondylitis or peripheral joints,
as patients present with psoriatic arthritis.
The different forms of SpA share a group of clinical characteristics; the most distinctive are inflammation of the axial joints (especially the sacroiliac joints ,SI),
asymmetric oligoarthritis (especially of the lower extremities),
dactylitis (sausage fingers) and enthesitis (inflammation at the insertion of the tendons and ligaments in the bone).
Additional features include skin and genital lesions,
ocular and intestinal inflammation,
an association with previous or ongoing infectious disorders,
positive family history,
elevated acute phase reactants and a strong association with human leukocyte antigen (HLA-B27) .
Management of SpA has changed dramatically in recent years due to biological drugs,
which have led to a large increase in the number of requests for MR assessment.
To understand this change,
it is essential to review the evolution over time of the classification criteria (Fig.1).
The NY criteria were born in 1984 for the diagnosis of AS and include clinical and radiological criteria
Clinical:
- back pain of at least 3 months that improves with physical activity and worsens with rest
- limitation of mobility of the lumbar spine in the frontal and sagittal planes.
- decreased thoracic expansion in relation to normal values for age and sex.
Radiological:
Radiological sacroiliitis is considered
- bilateral sacroiliitis at least grade 2 or
- unilateral grade 3 or 4
Different criteria were followed in time,
including now other entities of the Spa spectrum,
not only the AS.
In 2009 and coinciding with the appearance of biological therapy,
the Assessment of Spondyloarthropathy Association (ASAS) classification criteria for axial SpA and in 2011 for peripheral SpA arise.
They are applied to patients under 45 years of age with lumbar pain of more than 3 months duration as mandatory entry criteria and includes 2 arms: image and clinical.
- To fulfill the "image" arm,
it must have sacroiliitis or simple radiography according to modified NY criteria or by RM + presenting at least one of the characteristic features of SpA.
- In the clinical arm,
the patient must have HLA B27 positive + present at least 2 features of SpA,
without the image sacroilitis is mandatory.
This guide is very useful for the diagnosis of ankylosing spondylitis in cases that follow a typical clinical course with initial sacroiliac involvement following to the spine. But there is evidence that there may be cases in which clinical symptoms in the spine appear before sacroiliac are affected or even exclusive involvement of the spine. Furthermore,
acute inflammation in axial SpA affects only the spine and spares the SI joints in 23% ofcases,
so there is a need to better define the role of MRI in this group.
A group of 10 people including 8 rheumatologists and 2 radiologists, members of the ASAS held several workshops for the approval of a consensus that would improve the definition criteria of ankylosing spondylitis in the spine.
Some of their conclusions are commented further on.