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Development of a radiographic scoring tool for ankylosing spondylitis only based on bone formationAddition of the thoracic spine improves sensitivity to change.

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Arthritis & Rheumatism (Arthritis Care & Research)
Vol. 61, No. 6, June 15, 2009, pp 764 –771
DOI 10.1002/art.24425
© 2009, American College of Rheumatology
ORIGINAL ARTICLE
Development of a Radiographic Scoring Tool for
Ankylosing Spondylitis Only Based on Bone
Formation: Addition of the Thoracic Spine
Improves Sensitivity to Change
X. BARALIAKOS,1 J. LISTING,2 M. RUDWALEIT,3 J. SIEPER,3
AND
J. BRAUN1
Objective. The modified Stokes Ankylosing Spondylitis Spinal Score (mSASSS) quantifies radiographic changes in the
cervical spine (C-spine) and the lumbar spine (L-spine), but not in the thoracic spine (T-spine). Our objective was to study
the contribution of the lower part of the T-spine to structural damage in patients with ankylosing spondylitis (AS).
Methods. Radiographs of 80 AS patients obtained at baseline and after 2 years were scored by 2 readers using the
mSASSS. In addition, changes in the lower T-spine (T10 –T12) were quantified. On this basis, a new scoring tool was
developed: the Radiographic Ankylosing Spondylitis Spinal Score (RASSS). The RASSS includes 2 changes: no scoring
of erosions in order to confine the scoring to new bone formation, and no scoring of squaring in the C-spine for anatomic
and feasibility reasons.
Results. The mean ⴞ SD change was 0.9 ⴞ 2.5 units using the mSASSS and 1.6 ⴞ 2.8 units using the RASSS (P < 0.001).
Although the mSASSS identified new syndesmophytes in mean ⴞ SD 1.4 ⴞ 2.9 vertebral edges over 2 years, an additional
0.6 ⴞ 1.2 vertebral edges were seen in the lower T-spine. New syndesmophytes or ankylosis were found in 15 patients
(21.4%; 95% confidence interval [95% CI] 13.1–32.4%) in the C-spine/L-spine and in 6 patients (8.6%; 95% CI 3.8 –17.2%)
in the T-spine alone. The reliability of the RASSS and the agreement between readers was excellent.
Conclusion. The lower T-spine improves the sensitivity to change of scoring radiographic progression in AS. The tool
developed in this study, the RASSS, showed better face and content validity than the mSASSS and was proven to be
superior in the quantification of new bone formation in AS.
INTRODUCTION
Ankylosing spondylitis (AS) is a frequent chronic inflammatory rheumatic disease that affects the axial skeleton at
a young age (1), starting from the sacroiliac joints and later
potentially spreading to the entire spine (2). New bone
formation, syndesmophytes, and ankylosis of the vertebral
column, which are pathognomonic for the structural
changes occurring in AS, are used to assess the course of
the disease.
The gold standard for the assessment of chronic structural changes in AS are conventional radiographs (3,4),
1
X. Baraliakos, MD, J. Braun, MD: Rheumazentrum Ruhrgebiet and Ruhr-University Bochum, Herne, Germany; 2J.
Listing, PhD: German Rheumatism Research Center, Berlin,
Germany; 3M. Rudwaleit, MD, J. Sieper, MD: University
Medicine Berlin, Campus Benjamin Franklin, Berlin, Germany.
Address correspondence to J. Braun, MD, Rheumazentrum Ruhrgebiet, Landgrafenstrasse 15, 44652 Herne, Germany. E-mail: J.Braun@Rheumazentrum-Ruhrgebiet.de.
Submitted for publication September 17, 2008; accepted
in revised form February 2, 2009.
764
although magnetic resonance imaging (MRI) techniques
are also useful to assess spinal inflammation (2,5). Using
MRI, recent studies from Europe (6,7) and North America
(8,9) have shown that the lower half of the thoracic spine
(T-spine) is most frequently affected by active but also
chronic lesions in patients with AS.
It is of major interest in clinical studies and daily practice to know whether or not and how much radiographic
progression related to AS can be detected in individual
patients. These questions relate to the scoring systems
used. Chronic spinal changes in AS are currently quantified by the modified Stokes Ankylosing Spondylitis Spinal
Score (mSASSS) (10), an evaluated scoring system that is
currently regarded as the best available on a data-driven
basis (11). For the assessment of spinal radiographic progression in patients with AS, an observation period of 2
years is the shortest possible followup period based on the
reliability and sensitivity to change of the mSASSS (12).
The smallest detectable change (SDC) (13) is a measure
of a statistically significant radiographic change in individual patients beyond background noise in the case of a
paired reading of the films. The SDC has a better sensitiv-
New Scoring System for AS Based on New Bone Formation
765
ity to change than the frequently used smallest detectable
difference (SDD), which expresses the smallest difference
between 2 independently obtained measures that can be
interpreted as real (14). Because radiographic deterioration
is scored with the films compared side by side (paired
reading) and not independently in rheumatologic studies
(14), the SDD is less appropriate than the SDC for the
definition of cutoff levels for changes between measurements. Nevertheless, we have recently shown that counting new syndesmophytes between time points is even
more sensitive than the SDC or SDD for depicting radiographic deterioration in patients with AS (15).
A potential disadvantage of the mSASSS is that the
T-spine is not included, which is also true for other scoring systems (16). This is because of mainly technical reasons such as superimposition of the lungs in plain radiographs. Therefore, the reliability of scoring the T-spine has
remained insufficient to date (7). Thus, the most frequently
affected spinal region has not become part of scoring systems developed up to now. Because of this, many syndesmophytes may not have been detected in recent studies
(17–20). This may in part explain the relatively low sensitivity to change of the mSASSS (15).
Recent data based on the mSASSS suggest that the very
clinically efficacious tumor necrosis factor blockers do not
inhibit radiographic progression in patients with AS (18 –
20). Because the mean radiographic change has been reported to be less than 1 syndesmophyte (mSASSS scores
between 0.4 and 1.5 units over 2 years) (17,21), the sensitivity to change of the mSASSS has been questioned.
Furthermore, the face and construct validity of the
mSASSS may be criticized because a score of 1 contains a
mixture of osteodestructive (erosions) and osteoproliferative changes (squaring and sclerosis). Recent studies have
indicated that erosions occur in less than 5% of all radiographic changes that develop over 2 years (15) in patients
with AS. Furthermore, it was recently shown that the
scoring of squaring in the cervical spine (C-spine) has
problems on the basis of the anatomy of several cervical
vertebrae that already naturally appear squared; this gives
reason for false positive scores at this location (22).
The Outcome Measures in Rheumatology Clinical Trials
(OMERACT) filter (23) is an instrument used to evaluate
and compare different outcome methods for use in rheumatology. According to the OMERACT filter, 3 aspects
(discrimination/sensitivity to change, truth, and feasibility) should be investigated before a preference between
any proposed methods can be made.
The main objective of this study was to assess and quantify the additional information gained by inclusion of the
lower T-spine in the assessment of radiographic progression observed in patients with AS. Furthermore, on that
basis, we intended to possibly develop and evaluate a new
scoring tool that also takes into account the other problems
discussed above.
spine (L-spine) at 2 time points: the first clinical presentation (baseline) and 2 years later (2-year followup). All
radiographs were performed according to the standard
protocol used in our hospital. All of the patients included
in this study fulfilled the modified New York criteria for
AS (24). Radiographs were performed between January
1999 and December 2003 as part of a routine outpatient
clinic procedure. None of the patients were treated with
biologic agents. No other selection filters (level of disease
activity, clinical or laboratory parameters) were used for
selection.
After blinding of the radiographs for the patient’s identity and the time point of performance, all images of the
C-spine and L-spine were scored using the mSASSS, as
recently described in detail (10,15), by 2 experienced readers (JB, XB) in a blinded paired design (14). In addition, all
visible vertebral edges (VEs) of the lower part of the Tspine were scored and separately documented.
Radiographic studies of AS always involve missing data
and technical problems such as low quality of some images, overexposure or underexposure of films, or suboptimal positioning of the patients, leading to incomplete capturing of spinal segments and vertebrae (11,15). In the
present study, similar to recent proposals (11,15), we excluded images of patients with greater than 3 VEs missing.
In cases with ⱕ3 VEs missing, the missing VEs were replaced by the mean scores of the vertebrae of the same
spinal segment. The lower part of the T-spine and the
L-spine were handled as one spinal segment.
PATIENTS AND METHODS
Clinical parameters. Assessments of clinical parameters (Bath Ankylosing Spondylitis Disease Activity Index
[25], Bath Ankylosing Spondylitis Functional Index [26],
and Bath Ankylosing Spondylitis Metrology Index
Patients were retrospectively selected based on the availability of radiographs of the lateral C-spine and lumbar
Development of the Radiographic Ankylosing Spondylitis Spinal Score. When it became clear that the additional scores obtained from the lower T-spine improved
the sensitivity to change of the mSASSS, we decided to
develop a new scoring tool in order to further improve the
validity of the method. Therefore, we changed 2 further
aspects: 1) in order to confine the score to new bone
formation, we excluded all scorings of erosions in all spinal segments (15), and 2) in order to avoid false positive
scores, we excluded the scorings for squaring in the Cspine. The main reason for these modifications was a recent study showing that the scoring of squaring in the
C-spine is not reliable, with the exception of C5 and C6
(22). Since squaring in the C-spine is an infrequent event
(⬍1% of all scores) it is also scored in the T-spine, and
because of the better feasibility of handling all similar
spinal segments, we decided to omit the scoring of squaring for the entire C-spine.
The new tool was named the Radiographic Ankylosing
Spondylitis Spinal Score (RASSS) to stress the fact that
this is not a mixed score of osteodestructive and osteoproliferative lesions anymore, hereby distinguishing it from
the mSASSS (Table 1). The final step was then to score all
of the images a second time with this new score in order to
compare it with the current gold standard (the mSASSS)
and prove its feasibility.
766
Baraliakos et al
Table 1. Comparison of the 2 scoring systems that were evaluated in this study: the mSASSS and the RASSS*
mSASSS
View of image/sites scored
Assessed spinal segments
Cervical spine
Thoracic spine
Lumbar spine
Range of scoring system
Scoring definitions
0
1
2
3
RASSS
Lateral/anterior vertebral edges
Lateral/anterior vertebral edges
Lower edge of C2 to upper edge of T1
Not included
Lower edge of T12 to upper edge of S1
0–72
Lower edge of C2 to upper edge of T1
Lower edge of T10 to upper edge of T12
Lower edge of T12 to upper edge of S1
0–84
No change
Erosion, squaring, sclerosis for both
the cervical and lumbar spines
No change
No erosions scored, squaring only for
the thoracic and lumbar spines,
sclerosis scored for all sites available
Syndesmophytes
Bridging syndesmophyte/ankylosis
Syndesmophytes
Bridging syndesmophyte/ankylosis
* mSASSS ⫽ modified Stokes Ankylosing Spondylitis Scoring System; RASSS ⫽ Radiographic Ankylosing Spondylitis Spinal Score; C ⫽ cervical; T
⫽ thoracic; S ⫽ sacral.
[BASMI] [27], which include the tests for anteroposterior
[Schober] and lateral spinal mobility and standard laboratory parameters [C-reactive protein level, erythrocyte sedimentation rate]) were available for all patients at both
time points. The results of the anteroposterior and lateral
thoracolumbar mobility assessments were correlated with
the status and change scores of the radiographic evaluations.
Statistical analysis. Wilcoxon’s paired rank sum test
was used to compare the readings of the 2 scoring systems
between different time points. Pearson’s correlation coefficient was used to measure the association between the
radiographic data and the single clinical and laboratory
parameters. To measure the variability between single
readings of the change scores of the 2 readers, the interrater variance was estimated by means of analysis of variance. The intraclass correlation coefficients and their 95%
confidence intervals (95% CIs) were calculated to compare
the interrater variance with the variability between the
total scores of the patients. Similar to a recent modification
(15), the SDC (13) was calculated by taking into account
the number of readings available for the calculation. This
means that the calculation was based on 95% tolerance
limits, ensuring that ⬍5% of the changes greater than the
SDC were due to the measurement error and/or the uncertainty in the readings.
RESULTS
Additional information on status scores at baseline after inclusion of the lower part of the T-spine. Altogether,
80 patients who had appropriate available radiographs
were included in the study. The baseline demographic,
clinical, and radiographic data of the patients at baseline
and at followup are shown in Table 2.
The lower part of the T-spine was clearly visible and
could be assessed in 70 patients (88%), whereas the remaining 10 patients (12%) had to be excluded from the
analysis because less than 3 VEs were visible on their
films.
The most caudal VE that could possibly be detected was
the lower edge of the ninth thoracic vertebra (T9). ThereTable 2. Demographic, clinical, and radiographic
descriptions of the 70 patients included in the
assessment of the radiographic progression in
this study*
Assessment
Demographic characteristics
Age, years
Men, no. (%)
HLA–B27 positive, no. (%)
Symptoms duration, years
Clinical parameters at baseline
BASDAI
BASFI
BASMI
CRP level, mg/dl
Radiographic parameters
mSASSS
Baseline
Followup
RASSS
Baseline
Followup
Score in the cervical spine
Baseline
Followup
Score in the lumbar spine
Baseline
Followup
Score in the thoracic spine
Baseline
Followup
Value
37.3 ⫾ 10.4
46 (65.7)
61 (87)
10.8 ⫾ 8.6
4.6 ⫾ 2.2
3.9 ⫾ 2.6
2.8 ⫾ 2.0
10.1 ⫾ 14.9
8.1 ⫾ 14.6
9.0 ⫾ 12.9
9.8 ⫾ 16.0
11.4 ⫾ 14.8
4.6 ⫾ 9.1
5.1 ⫾ 11.8
3.5 ⫾ 7.6
3.9 ⫾ 9.9
1.7 ⫾ 3.0
2.3 ⫾ 3.2
* Values are the mean ⫾ SD unless otherwise indicated. BASDAI ⫽
Bath Ankylosing Spondylitis Disease Activity Index; BASFI ⫽ Bath
Ankylosing Spondylitis Functional Index; BASMI ⫽ Bath Ankylosing Spondylitis Metrology Index; CRP ⫽ C-reactive protein;
mSASSS ⫽ modified Stokes Ankylosing Spondylitis Spinal Score;
RASSS ⫽ Radiographic Ankylosing Spondylitis Spinal Score.
Status instruments
Variance between
patients
Interrater variance
ICC (95% CI)
Agreement between
readers, no. (%)
(n ⫽ 70)
Disagreement between
readers, no. (%)
(n ⫽ 70)
ⱕ2 score units
⬎2 score units
* Data are shown as the variance between patients and interrater variance with the corresponding intraclass correlation coefficients (ICCs), including agreement and disagreement between readers.
mSASSS ⫽ modified Stokes Ankylosing Spondylitis Spinal Score; RASSS ⫽ Radiographic Ankylosing Spondylitis Spinal Score; 95% CI ⫽ 95% confidence interval.
† ICC (95% CI).
13 (18.6)
3 (4.3)
12 (17.1)
2 (2.9)
23 (32.9)
8 (11.4)
20 (28.6)
7 (10.0)
12 (17.1)
4 (5.7)
13 (18.6)
7 (10.0)
0.31 (0.23–0.45)†
0.950 (0.904–0.974)
56 (80)
1.47
0.995 (0.990–0.997)
39 (55.7)
0.99
0.996 (0.992–0.998)
43 (61.4)
0.80
0.996 (0.993–0.998)
54 (77.1)
255.21
235.98
212.35
Baseline
Followup
1.01
0.996 (0.992–0.998)
50 (71.4)
5.93
298.56
Followup
mSASSS
Change scores
RASSS
Baseline
Additional information on change scores of radiographic progression in the 2-year followup after inclusion
of the lower part of the T-spine. The radiographic progression after 2 years showed a mean ⫾ SD change of 0.9 ⫾ 2.5
units in the mSASSS and 1.6 ⫾ 2.8 units in the RASSS
(P ⬍ 0.001). When assessing each spinal region separately,
the mean ⫾ SD RASSS change was 0.5 ⫾ 2.9 units in the
C-spine alone, 0.4 ⫾ 2.2 units in the L-spine alone, and
0.6 ⫾ 3.3 units in the lower part of the T-spine alone
within the 2-year followup period.
At followup, new syndesmophytes were depicted in
mean ⫾ SD 1.4 ⫾ 2.9 VEs per patient when using the
mSASSS, and in 0.6 ⫾ 1.2 VEs per patient in the additionally analyzed lower edge of T10 to the upper edge of T12
(Figure 2).
In the analysis based on single VEs, the occurrence of
AS-specific progression such as development of new syn-
mSASSS
Reliability of the readings for both scoring systems.
The interrater variances of the status and the change scores
for both the mSASSS and the RASSS were very low, indicating excellent reliabilities for both scoring systems (Table 2). The low interrater variances also corresponded to
very low SDC values of 1.1 for the mSASSS and 1.3 for the
RSASSS, suggesting that a progression of ⱖ2 units represents a relevant radiographic change. The detailed comparison of the 2 scoring systems, including data on the
agreement/disagreement between readers, is shown in Table 3 and Figure 1.
Table 3. Detailed data on the reliability of the readings for both scoring systems*
Differences in the outcome of radiographic change after
inclusion and exclusion of erosions and vertebral squaring in the C-spine of patients with AS. Overall, 827 cervical VEs were available for analysis at baseline. Of those,
a score of 1 was found in 16 VEs. In those VEs, squaring
was identified in only 3 cases (0.4%). Furthermore, only
1% of the VEs showed deterioration from no damage to
erosions after 2 years. Inclusion or exclusion of scorings
for erosions and of scores for squaring in the C-spine did
not change the overall score for radiographic deterioration:
the mean ⫾ SD RASSS change was 1.7 ⫾ 3.1 units with the
scorings and 1.6 ⫾ 2.8 units without the scorings (P ⬎
0.05).
RASSS
fore, the maximal possible information on radiographic
progression that could have possibly been obtained was on
6 additional VEs (lower edge of T9 through upper edge of
T12). However, the lower edge of T9 was assessable in
only 9 patients (12.9%), and the upper edge of T10 was
assessable in only 18 (25.7%) of 70 patients, leading to ⬎3
missing sites in the T-spine in the majority of the patients.
In contrast, all other VEs from the lower edge of T10 to the
upper edge of T12 were visible in ⬎50% of the patients.
Their inclusion significantly added information to the total amount of radiographic damage detected with mean ⫾
SD 3.1 ⫾ 0.4 VEs per patient, thus including all patients in
the evaluation. The inclusion of the additional VEs in the
analysis increased the range of the scoring system from
0 –72 units in the mSASSS to 0 – 84 units in the RASSS
(Table 1).
0.41 (0.31–0.59)†
0.949 (0.903–0.974)
54 (77.1)
767
7.70
New Scoring System for AS Based on New Bone Formation
768
Baraliakos et al
Correlation of radiographic scores and clinical assessments. The baseline values of the mSASSS and RASSS
correlated significantly (r ⫽ 0.984, P ⬍ 0.001). Furthermore, there was a statistically significant correlation between the RASSS and the BASMI (r ⫽ 0.46), but also
between the mSASSS and the BASMI (r ⫽ 0.49) at baseline
(P ⬍ 0.001 for both). Regarding change scores, there was a
statistically significant correlation between the mSASSS
change and the RASSS change (r ⫽ 0.87, P ⬍ 0.001).
However, there was no statistically significant correlation
between radiographic scores and clinical or laboratory parameters (data not shown).
DISCUSSION
Figure 1. Differences in change scores between the modified
Stokes Ankylosing Spondylitis Spinal Score (mSASSS) and the
Radiographic Ankylosing Spondylitis Spinal Score (RASSS)
based on the individual scores of the 2 readers. The x-axis shows
the difference between the change scores over 2 years (RASSS
change scores minus mSASSS change scores). The y-axis shows
the number of patients corresponding to those differences. On the
left side of the dotted line, the difference in change scores indicates superiority of the mSASSS to detect radiographic deterioration over time, whereas on the right side of the dotted line, the
difference in change scores shows superiority of the RASSS to
detect radiographic deterioration over time. The RASSS has a
higher sensitivity to change because the majority of the differences are on the right side of the dotted line.
To our knowledge, this is the first study to examine and
quantify the radiographic changes in the lower part of the
T-spine using conventional radiographs of patients with
AS. On this basis, and after taking into account recent
publications on the subject, we developed a new tool for
scoring radiographic progression in patients with AS that
is purely based on new bone formation: the RASSS.
As shown in the present study, the lower part of the
T-spine is visible in the vast majority of spinal radiographs
obtained in daily routine in Germany. This is probably due
to historical recommendations: some decades ago, Dihlmann taught about specifically assessing the region of the
lower T-spine and the upper L-spine in patients with AS,
which is still recommended by the German Society of
desmophytes or progression from syndesmophytes to ankylosis occurred mean ⫾ SD 0.04 ⫾ 0.3 times per VE in the
C-spine and L-spine and 0.02 ⫾ 0.22 times per VE in the
lower T-spine (P ⬎ 0.05 between segments).
Importantly, on the patient level, development of new
syndesmophytes/ankylosis was seen in 15 (21.4%) of 70
patients (95% CI 13.1–32.4%) in the C-spine and L-spine
and in 6 (8.6%) of 70 patients (95% CI 3.8 –17.2%) in the
T-spine alone; 4 patients showed such changes in all 3
spinal segments (C-spine, L-spine, and T-spine).
Feasibility of evaluation of changes in the lower part of
the T-spine. The mean ⫾ SD time for the scoring of the
images using the mSASSS was 91.6 ⫾ 60.2 seconds per
patient for the C-spine and L-spine, and 18.8 ⫾ 10.1 seconds for the lower part of the T-spine. Therefore, the
mean ⫾ SD time of scoring the films of a single patient was
usually ⬍2 minutes, with a minor increase in time for the
lower T-spine.
Radiation exposure. The radiation exposure (dosis/surface product) calculated for the patients remained below
the limit (800 cGy/cm2) prescribed by the guidelines of the
responsible authorities (Bundesamt für Strahlenschutz)
(28), with a value of 616.94 cGy/cm2.
Figure 2. Example of the development of new syndesmophytes in
the lower part of the thoracic spine and in the lumbar spine 2
years after baseline. Th ⫽ vertebral body in the thoracic spine; L ⫽
vertebral body in the lumbar spine.
New Scoring System for AS Based on New Bone Formation
Rheumatology (29). Since we cannot be sure that this is
also the case in other radiologic departments in the world
where the radiograph is often centered lower with tighter
collimation so that only T12 is included on the image, our
data suggest that it may be advisable to change the acquisition technique in order to be able to apply the new
scoring system. The required technique is described in the
Patients and Methods section. Generally, altering the beam
and centering and opening the collimation requires only a
minor change in practice, resulting in a slightly inferior
projection of the lower L-spine without limiting AS-related changes for scoring.
In general, to be able to score with the RASSS, the
segments T10 (lower edge) to T12 (upper edge), in addition
to the C-spine and the L-spine, need to be assessed on the
radiographs. Because spinal segments located more cranially are not clearly visible (15), vertebrae such as the lower
edge of T9 and the upper edge of T10, although visible in
some images, finally had to be excluded from the score.
Whether it will be technically possible and statistically
necessary to include more vertebrae of the T-spine will be
subject to future studies. In any case, at the end of the first
part of this study, it seemed obvious that the lower part of
the T-spine should be included in the assessment and the
scoring of the lateral lower spine. On this basis, we believed that it was time to develop a new scoring system
and not to modify the mSASSS a second time (10,30).
Therefore, we proposed to score radiographic progression
in AS with the new scoring tool, the RASSS, which, as
shown in this study, performs superior to the mSASSS.
The general principle of scoring a mixture of osteoproliferative changes such as squaring, sclerosis, syndesmophytes formation, and ankylosis with osteodestructive
changes such as erosions has no convincing face and content validity, since a development from an erosion to a
syndesmophyte is a rare event, if it occurs at all. Theoretically, 2 scoring systems, one for osteoproliferative
changes and one for osteodestruction, would be ideal.
However, since erosions tend to occur infrequently, in less
than 5% of all radiographic changes as shown only recently (15), it appeared straightforward to omit that position.
According to the data from a recent study in Korea (22),
several vertebrae of the C-spine already appear squared by
the nature of their anatomy. Since this was in accordance
with our own subjective experience, we first decided to
propose to only score the 5th and 6th cervical vertebrae in
the RASSS without any further analysis of our data on this
subject. Because we then calculated that squaring in the
C-spine occurred in less than 1% of the VEs assessed, we
finally decided to exclude all scorings of squaring in the
C-spine from the final analysis. We also believe that this
improves the feasibility and simplicity of the scoring system.
The status and change scores of the RASSS have been
compared with the original mSASSS not only on a numerative basis of score units, but also based on the main
aspects of the OMERACT filter (truth, discrimination/sensitivity to change, and feasibility) (23).
With respect to the aspect of truth, a major argument is
that our results are very much in line with recent reports
769
on the relative frequency of inflammatory and structural
spinal lesions in patients with AS, as depicted by MRI,
showing that spinal lesions mostly occur in the lower part
of the T-spine (6 –9). In the present study, when only the
C-spine and the L-spine were scored, approximately 20%
of the patients showed definite AS-related changes such as
syndesmophytes and ankylosis, again similar to previous
reports (15). This proportion increased to 30% of the patients when the lower part of the T-spine was added.
Similar results were obtained when the analysis was performed on the basis of spinal segments: the mean change
scores were higher in the lower part of the T-spine as
compared with the changes in the rest of the spine.
Similar to the mSASSS, the RASSS is also mainly based
on the most disease-specific changes in AS (15): syndesmophytes. Therefore, a change of ⱖ2 units in the RASSS
represents a significant radiographic change. Importantly,
this does not necessarily indicate the presence of new
syndesmophytes, since 2 scores of a single RASSS unit
would also add up to a score of 2. This score represents a
relevant cutoff for the assessment of radiographic progression in AS patients after 2 years. On this basis, a deterioration of structural damage occurred in more than 80% of
the patients in our cohort.
The truth aspect was also assessed by correlating the
change scores of the scoring systems to clinical parameters. Similar to most previous studies, no significant correlations were found (11,15,18,20), although another study
suggested a closer link between radiographic damage and
spinal mobility as measured by the BASMI (31). One possible reason for a partial disconnect is that physical function in AS is also independently determined by disease
activity and not only radiographic damage of the spine
(32).
Regarding the OMERACT filter aspect discrimination,
the mean radiographic progression was significantly increased when using the RASSS as compared with the
mSASSS. This might be related to the significantly higher
ability of the RASSS to depict patients with development
of new syndesmophytes, the most valid way to characterize cohorts of AS patients in terms of structural damage
(15).
Finally, for the feasibility aspect, the addition of the
lower part of the T-spine only marginally added time to
the act of scoring in the RASSS as compared with the
mSASSS. Overall, the additional seconds needed to score
the lower part of the T-spine do not seem to matter much
with respect to the gain in sensitivity to change. Furthermore, no additional time was needed to perform the radiographs of the lower part of the T-spine, since no extra
radiographs were needed.
The fact that in other departments, performance of routine radiographs of the L-spine does not include the lower
part of the T-spine may limit the ability to use the RASSS
in those patients. However, in a setting of clinical studies,
the inclusion of this part of the spine may be arranged as a
part of the imaging protocol. It is worth mentioning that
overall, the comparison between images with and without
inclusion of the T-spine may lead to a slightly inferior
projection of the lower L-spine. However, this will not
have a major influence on the results, and we think that
770
Baraliakos et al
this small sacrifice is worth it because of the gain in validity and sensitivity to change by using the RASSS.
Subsequently, a further limitation not only of the
present study but for all assessments of radiographic deterioration in the spine of AS patients is the fact that we
are for technical reasons still not able to completely assess
the lower half of the T-spine, since we are aware that the
regions of T6 –T9 are also frequently affected (6). Therefore, we do not think that this is the end of all efforts to
improve the assessment of structural damage in AS, but we
do believe that this step performed here with this data is
the best we can currently do with the available technique.
In conclusion, the inclusion of the lower part of the
T-spine significantly increases the sensitivity to change
when scoring radiographic damage in AS because more
syndesmophytes are potentially scored. The new tool, the
RASSS, has better face and content validity than the
mSASSS. Overall, it proved to be clearly superior for the
assessment of structural damage in patients with AS. The
RASSS should be further evaluated in clinical trials and
cohort studies of patients with AS.
AUTHOR CONTRIBUTIONS
Dr. Braun had full access to all of the data in the study and takes
responsibility for the integrity of the data and the accuracy of the
data analysis.
Study design. Baraliakos, Braun.
Acquisition of data. Baraliakos, Rudwaleit, Sieper.
Analysis and interpretation of data. Baraliakos, Listing, Braun.
Manuscript preparation. Baraliakos, Listing, Sieper, Braun.
Statistical analysis. Baraliakos, Listing, Braun.
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development, spina, scoring, change, sensitivity, radiographic, tool, thoracica, formationaddition, improve, bones, base, ankylosis, spondylitis
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