ASAS CLassification of Axial SpondyloarthritiS Inception Cohort in the Netherlands

The Assessment of SpondyloArthritis international Society (ASAS) group has
developed classification criteria for axial spondyloarthritis (axSpA) that
allow the inclusion of patients with an early form of disease that is not yet
clearly visible on plain radiography. These criteria include both an *imaging
arm*, that incorporates either radiographic sacroiliitis or magnetic resonance
imaging (MRI) features of inflammation in the sacroiliac joints (SIJ) plus one
clinical feature of spondyloarthritis (SpA), and a *clinical arm* that requires
the presence of human leukocyte antigen-B27 (HLA-B27) plus 2 clinical features
of SpA. The sensitivity and specificity of these criteria for axSpA were 83%
and 84%, respectively, in patients with undiagnosed chronic back pain and
suspicion of SpA. The external standard for evaluation of these criteria was
the rheumatologist expert opinion of the SpA diagnosis after incorporating lab
and imaging data with clinical evaluation.

Since their introduction, some have raised concerns regarding the ASAS
classification criteria as substantial differences in the prevalence estimates
of axSpA have been found. One of these concerns are that the criteria may have
been misused as a checklist of SpA features to diagnose patients rather than
following a diagnostic process of clinical reasoning based on all available
information by an experienced clinician rheumatologist who then formulates a
final diagnostic opinion before the classification criteria are applied.

Despite all concerns, a five-year follow-up of the ASAS classification cohort
has reported high positive predictive value of the axSpA criteria with no
differences between the clinical and the imaging arm. However, more than half
of the collected patient information was obtained by telephone interviews.

It has been suggested that further education regarding appropriate
ascertainment of SpA features and evaluation of imaging might help to reduce
misclassification and to prevent that the criteria are inappropriately used as
a basis for diagnostic evaluation of SpA. With effective medication now
available for several years, and effectiveness being particularly apparent in
early disease, reducing diagnostic delay is a priority.

A joint meeting of the ASAS and the SpA Research and Treatment Network
(SPARTAN) executive boards has recommended that the ASAS classification
criteria undergo further validation in a prospective cohort in North American
(United States and Canada) and in a prospective cohort in Europe and other
parts of the world of patients presenting with undiagnosed active chronic back
pain to rheumatologists. Other differentiating features for this study, as
compared to the original ASAS classification criteria study, will be 1) central
image review and education on MRI and radiography for local investigators and
2) the comparison of the final diagnosis of the local rheumatologists with a
central clinical committee diagnosis as applied for new classification criteria
for systemic sclerosis and for SLE. This would serve to educate both
rheumatologists and radiologists in evaluating imaging for the diagnosis of
axSpA and to enhance confidence in the external standard determination of the
diagnosis of axSpA.

Primary study objective
To validate the performance of the current ASAS classification criteria in a
prospective combined cohort of patients presenting to a rheumatologist in North
America, Europe, and other parts of the world with undiagnosed current back
pain of >=3 months duration with onset <=45 years of age. If a specificity of
>=90% and a sensitivity of >=75% of the original ASAS criteria will be found in
the study, the ASAS criteria will be considered validated and no further
analyses will be done. Only if the primary objective is not met, refinements of
the criteria will be made and tested.

Secondary study objectives
1. To compare the ascertainment of sacroiliitis by MRI and the confidence of
this ascertainment by local investigators at sites across North America and
worldwide before and after interactive educational intervention. The
educational intervention with the local investigators will consist of formal
reporting, extensive DICOM-image annotation, and live case discussion provided
by the central readers. The central readers are musculoskeletal radiologists
and rheumatologists with extensive expertise (>5 years* experience) in the
assessment of axSpA.
2. To compare the final diagnosis of the local rheumatologists, which is made
after being informed about and after having discussed the imaging findings by
the central readers, with the diagnosis made by the central clinical committee.

Tertiary study objective
To determine the predictive validity of the ASAS classification criteria (also
split by imaging and clinical arm) over a five-year period.

Observational, longitudinal (visit at baseline and 5 years), multi-centric,
worldwide study. This protocol applies to centres in the Nederlands.

The burden can be considered to be very low. Information is obtained from
patient records or the treating physician at baseline and 5-years follow-up.
Patients receive usual care and they will not receive any intervention. Since
the nature of this study is observational, and the burden on the participants
is very low, there will not be any risks in taking part in this study.