What are the classification criteria for axSpA/AS?
Diagnostic and classification criteria are very important to institute in clinical medicine. Diagnostic criteria are broad and heterogenous; they include subjective symptoms, physical exam findings and objective tests that are used routinely in the clinic to help diagnose a condition and guide patient’s care. Classification criteria are usually standardized and homogenous; while some clinicians use them to aid in patient care, they are intended to create well-defined patient cohorts for clinical research. There are currently no diagnostic criteria in the field of axial spondyloarthritis. We list below several classification criteria, the most commonly used are the modified New York and the ASAS criteria.
In 1961, criteria were defined for the first time to classify Ankylosing Spondylitis; it was known as Rome criteria (Kellgren 1963). In this set of criteria, no correction was made for the effects of age and sex on chest and spinal mobility. Although the radiographic criterion was given a greater weight than the clinical criteria (3 times), a diagnosis of AS was still possible based solely on clinical criteria, without any radiographic evidence.
In 1966, the New York criteria (Bennett and Wood 1968) were introduced, which tweaked some of the Rome criteria. In the New York criteria, it was mandatory to have a radiographic criterion +/- clinical criteria. The presence of clinical criteria along with the radiographic one would give a diagnosis of definite AS; while the absence of clinical criteria would give a diagnosis of probable AS. In the clinical criteria, major changes were specifying spine planes where the motion is limited, quantifying the limitation in chest expansion, and omission of the iritis/eye inflammation criterion that was present in the Rome criteria.
1966 New York criteria for Ankylosing Spondylitis (Bennett and Wood 1968)
- Limitation of motion of the lumbar spine in all three planes: anterior flexion, lateral flexion, and extension
- History or the presence of pain at the dorso-lumbar junction or in the lumbar spine
- Limitation of chest expansion to 1 in. (2.5 cm) or less, measured at the level of the fourth intercostal space
Radiologic criteria: (SI joint radiographs were given numerical scores depending on the severity of the sacroiliitis)
- Grade 0: normal
- Grade 1: some blurring of the joint margins – suspicious
- Grade 2: minimal sclerosis with some erosion
- Grade 3: definite sclerosis on both sides of the joints OR severe erosions with widening of joint space with or without ankylosis
- Grade 4: complete ankylosis
*In order to meet the definite AS diagnosis, a patient would have to fulfill any of the following:
– Grade 3 or 4 bilateral sacroiliitis with at least one clinical criterion
– Grade 3 or 4 unilateral scroiliitis with Clinical criterion #1 (limitation of spine movement in all three planes) or with both clinical criteria #2 & #3 (pain and limitation of chest expansion)
– Grade 2 bilateral sacroIliitis with Clinical criterion #1 (limitation of spine movement in all three planes) or with both clinical criteria #2 & #3 (pain and limitation of chest expansion)
*In order to meet the probable AS diagnosis, a patient would have grade 3-4 bilateral sacroiliitis without any clinical criteria.
In 1984, the modified New York criteria (van der Linden 1984) for AS classification were published. This time pain was more precisely described, and both age and sex were taken into consideration when assessing limitation in chest expansion; stating that normograms corrected for age and sex should be used, without giving exact normal range values.
1984 modified New York criteria for Ankylosing spondylitis (van der Linden 1984)
- Low back pain and stiffness for more than 3 months which improves with exercise but is not relieved by rest.
- Limitation of motion of the lumbar spine in both the sagittal and frontal planes.
- Limitation of chest expansion relative to normal values corrected for age and sex
- Sacroiliitis grade 2 bilaterally or sacroiliitis grade 3-4 unilaterally
Grade 0: normal
Grade 1: suspicious – patchy periarticular osteoporosis
Grade 2: minimal – loss of definition at the edge of the joints, some sclerosis, minimal erosion
Grade 3: definite – definite sclerosis on both sides of the joints, blurring and indistinct margins, loss of joint space
Grade 4: ankylosis – complete fusion of the joint
*Definite AS diagnosis is met if the radiologic criterion is associated with at least one clinical criterion.
In the early 2000s, a new term was introduced which is non radiographic axial spondyloarthritis, where patients have symptoms of inflammatory back pain but no definite xray findings of sacroiliitis. While the modified New York criteria only targeted radiographic Ankylosing Spondylitis, there was a need to develop new classification criteria that encompass both entities of axial spondyloarthritis, whether radiographic or non-radiographic. For the first time, other imaging modalities like MRI findings, HLA B27 positivity, and miscellaneous spondyloarthritis features were included in the new classification criteria, developed by The Assessment of Spondyloarthritis International Society (ASAS) and called ASAS criteria (Rudwaleit 2009).
The Assessment of Spondyloarthritis International Society (ASAS) criteria (Rudwaleit 2009)
In order to meet the ASAS criteria, any patient under 45 years old of age with lower back pain of 3 months duration must have:
1. Radiological diagnosis of sacroiliitis plus one or more features of spondyloarthritis
2. HLA B27 plus two or more features of spondyloarthritis
Radiologic diagnosis of sacroiliitis is defined as:
- Active/acute inflammation in the MRI highly suggestive of sacroiliitis due to SpA
- Radiological sacroiliitis defined according to the New York criteria (grade >2 bilateral or grade 3-4 unilateral)
MRI findings of sacroiliitis are described as:
- The presence of active lesions at the SI joints
- Bone marrow edema on STIR or osteitis on T1 are suggestive of spondyloarthritis as long as they affect the subchondral periarticular areas of the bone marrow
- Disturbance of signal needs to be present in at least two consecutive cuts (if only one active lesion)
- If there are more than one active lesion, then one cut is enough
- Isolated synovitis, enthesitis or capsulitis without bone marrow edema or osteitis is not enough
- Structural lesions that reflect prior inflammation (fat deposits, erosions, sclerosis or ankylosis) without active lesions are not enough
Features of Spondyloarthritis were defined as:
- Low inflammatory pain
- Crohn/ulcerative colitis
- Good response to NSAID
- Family history of SpA
- positive HLA-B27
- High CRP
While the newer ASAS criteria enable rheumatologists to capture a new subset of patients, mainly non-radiographic spondyloarthritis patients, it does have some limitations. Bone marrow edema can be non-specific; and it’s presence does not necessarily mean that patients have spondyloarthritis; thus clinical context is very important. ASAS criteria only mentions SI joint MRI, without including spinal MRI, which could be missing some valuable information. Lastly, relying heavily on HLA B27 positivity could lead to mis-classification, especially in ethnicities where HLA B27 is highly prevalent, and when combining it with two other soft SpA features.
- Aggarwal et al. Distinctions between diagnostic and classification criteria? (2015) Arthritis Care & Research Vol. 67, No. 7, July 2015, pp 891–897
- Bennett, P. H., and Burch, T. A. (1968) Idem, pp. 305-313 – and Wood, P. H. N. (1968) Idem, p. 456
- Kellgren, J.H., Jeffrey, M. R., and Ball, J. (eds) (1963) “The Epidemiology of Chronic Rheumatism”. Vol. 1, p. 326. Blackwell, Oxford
- Rudwaleit M, van der Heijde D, Landewe R, Listing J, Akkoc N, Brandt J, et al. The development of Assessment of SpondyloArthritis international Society classification criteria for axial spondyloarthritis (part II): validation and final selection. Ann Rheum Dis. 2009;68(6):777–83.
- van der Linden S, Valkenburg HA, Cats A. Evaluation of diagnostic criteria for ankylosing spondylitis. A proposal for modification of the New York criteria. Arthritis Rheum. 1984;27(4):361-8.
Mohamad Bittar, MD, University of Tennessee Memphis
Last modified 02/11/20