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Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. Acknowledgements
  10. REFERENCES

Objective

Anemia is a common complication in patients with inflammatory diseases such as ankylosing spondylitis (AS). This post hoc analysis of a large, randomized, placebo-controlled trial examined the effect of infliximab on hemoglobin levels, physical function, and fatigue in patients with AS.

Methods

Patients received infliximab 5 mg/kg (n = 188) or placebo (n = 68) at weeks 0, 2, 6, 12, and 18. Hemoglobin, interleukin-6 (IL-6), and C-reactive protein (CRP) levels, fatigue (visual analog scale [VAS]), physical function (Bath Ankylosing Spondylitis Functional Index [BASFI]), and disease activity were evaluated at baseline and week 24. Anemia was defined as a hemoglobin level <12 gm/dl for women and <13 gm/dl for men.

Results

At baseline, 11 placebo group patients (16.2%) and 37 infliximab group patients (19.7%) had anemia. Of these, more infliximab-treated patients achieved normal hemoglobin levels at week 24 compared with patients receiving placebo (70.3% versus 27.3%; P = 0.0155). Infliximab-treated patients had significant improvements in mean hemoglobin concentration (0.7 gm/dl versus −0.3 gm/dl), BASFI score (−2.1 versus −0.2), and fatigue VAS score (−2.4 versus −0.4) compared with placebo patients (P < 0.001). Multiple regression analyses showed that improvements in hemoglobin level were significantly and independently associated with improvements in physical function and fatigue. Infliximab-treated patients with elevated CRP or IL-6 levels at baseline were more likely than those with low levels to have improvement in hemoglobin levels.

Conclusion

Infliximab treatment significantly decreased the proportion of AS patients with anemia and improved hemoglobin levels compared with placebo. Improvement in hemoglobin level was independently associated with improvements in physical function and fatigue.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. Acknowledgements
  10. REFERENCES

Ankylosing spondylitis (AS) is a chronic, progressive disease characterized by inflammation of entheses, leading to new bone formation, syndesmophytes, and ankylosis of joints, primarily in the axial skeleton (1–3). Patients with AS often have associated peripheral arthritis, enthesitis, osteoporosis, or extraarticular involvement such as uveitis, psoriasis, or inflammatory bowel disease (1). Anemia is also a common complication of chronic inflammatory diseases, and in patients with rheumatoid arthritis (RA) it has been associated with increased disease activity, pain, and fatigue (4). These symptoms and complications of AS can significantly affect a patient's quality of life, as demonstrated by the high rates of disability and unemployment found in patients with AS when compared with the general population (5). The exact prevalence of anemia in patients with AS is unknown, but ∼50% of patients with RA have anemia (6).

There are multiple potential causes of anemia in patients with AS, including anemia of chronic disease (also known as anemia of inflammation). The proinflammatory cytokines tumor necrosis factor α (TNFα) and interleukin-6 (IL-6) have been implicated in the pathogenesis of AS (7). These cytokines also play a role in the pathogenesis of anemia of chronic disease through their inhibitory effects on erythropoiesis (6, 8), which may be mediated through the recently discovered acute-phase protein hepcidin (9, 10). Another possible cause of anemia is the use of nonsteroidal antiinflammatory drugs (NSAIDs), which are considered first-line therapy in AS (11) and can cause gastrointestinal bleeding (12).

Treatment with infliximab, a monoclonal anti-TNFα antibody, in the Ankylosing Spondylitis Study for the Evaluation of Recombinant Infliximab Therapy (ASSERT) led to significant improvements in disease activity, physical function, quality of life (13), and spinal inflammation (14), as well as decreased serum levels of IL-6 and C-reactive protein (CRP) (15), a marker of inflammation that has also been associated with anemia (8). In the present analysis, data from ASSERT were used to evaluate the effect of infliximab on anemia in patients with AS, as well as the association of hemoglobin levels with physical function and fatigue.

PATIENTS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. Acknowledgements
  10. REFERENCES

Study design

The patient eligibility, study design, and primary results of ASSERT have been previously described (13). Briefly, patients with AS were randomly assigned to receive placebo or infliximab 5 mg/kg at weeks 0, 2, 6, 12, and 18. Hemoglobin levels were evaluated at baseline and week 24. The proportion of patients who achieved or maintained normal hemoglobin levels at week 24 and the proportion of patients who had any improvement in hemoglobin from baseline to week 24 (regardless of whether they achieved normal levels) were determined. Anemia was defined using the World Health Organization criteria of a hemoglobin level <12 gm/dl for women and <13 gm/dl for men. Physical function (Bath Ankylosing Spondylitis Functional Index [BASFI] score), fatigue (visual analog scale [VAS] score), and disease activity (Bath Ankylosing Spondylitis Disease Activity Index [BASDAI] score) were assessed at baseline and week 24. Clinical response was defined as a 20% improvement of the Assessment of SpondyloArthritis International Society criteria (ASAS20) at week 24.

Statistical analysis

Descriptive statistics, including means and SDs for continuous variables and counts and percentages for discrete variables, were used to summarize the data. Statistical tests on the differences between treatment groups were performed using an analysis of variance on the van der Waerden scores, and categorical data were tested using chi-square tests. Logistic regression analyses were used to estimate the odds ratios (ORs) and 95% confidence intervals (95% CIs) of an improvement in hemoglobin levels for patients with elevated or normal CRP levels at baseline (≤0.5 mg/dl and >0.5 mg/dl, respectively). A similar analysis was performed for IL-6, with patients divided into categories of IL-6 levels based on the median IL-6 value at baseline (≤7.46 pg/ml and >7.46 pg/ml, respectively). A multiple linear regression model that included age, sex, disease duration, week-24 levels of IL-6 and CRP, and change from baseline to week 24 in BASDAI score was used to evaluate the association between improvement in hemoglobin levels and physical function (BASFI score). A similar model that included age, sex, disease duration, week 24 levels of IL-6 and CRP, and change from baseline to week 24 in morning stiffness (part of the BASDAI score) was used to evaluate the association between improvement in hemoglobin levels and fatigue.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. Acknowledgements
  10. REFERENCES

Baseline characteristics

This post hoc analysis included all patients who had available hemoglobin data at both baseline and week 24 (placebo n = 68, infliximab n = 188) (Table 1). Baseline characteristics were similar between the treatment groups. In total, 11 (16.2%) of the placebo group patients and 37 (19.7%) of the infliximab group patients had anemia at baseline. Patients with anemia had significantly higher levels of CRP and IL-6 at baseline than patients with normal hemoglobin levels (median 3.9 versus 1.4 mg/dl and 12.6 versus 6.5 pg/ml, respectively; P < 0.0001 for both).

Table 1. Baseline demographics and disease characteristics*
 Placebo (n = 68)Infliximab (n = 188)
  • *

    Values are the mean ± SD unless otherwise indicated. VAS = visual analog scale; BASFI = Bath Ankylosing Spondylitis Functional Index; CRP = C-reactive protein; IL-6 = interleukin-6.

Male, no. (%)61 (89.7)149 (79.3)
Age, years40.0 ± 9.739.3 ± 10.5
Disease duration, years11.5 ± 8.010.3 ± 8.7
Fatigue VAS6.4 ± 2.26.7 ± 2.0
BASFI score5.9 ± 2.25.7 ± 1.9
Hemoglobin level, mg/dl14.0 ± 1.413.6 ± 1.4
CRP level, mg/dl2.2 ± 2.12.5 ± 2.8
IL-6 level, pg/ml10.0 ± 11.313.6 ± 20.5
Patients with anemia, no. (%)11 (16.2)37 (19.7)

Effects of infliximab on hemoglobin levels and clinical assessments at week 24

Patients treated with infliximab demonstrated statistically significant improvements in mean hemoglobin levels (0.7 gm/dl versus −0.3 gm/dl; P < 0.001), mean BASFI score (−2.1 versus −0.2; P < 0.001), and mean fatigue VAS score (−2.4 versus −0.4; P < 0.001) at week 24 when compared with patients in the placebo group. Among patients who had anemia at baseline, a greater proportion of patients in the infliximab group achieved normal hemoglobin levels at week 24 than patients in the placebo group (70.3% versus 27.3%; P = 0.0155) (Figure 1). Among patients who did not have anemia at baseline, 98.0% who received infliximab maintained normal hemoglobin levels at week 24, compared with 89.5% who received placebo (P = 0.0140) (Figure 1). The proportion of patients who did not have anemia at baseline and demonstrated some improvement in hemoglobin level was also greater in the infliximab group than in the placebo group (66.9% versus 31.6%; P < 0.0001). Overall, and irrespective of anemia status, 70.2% of patients treated with infliximab demonstrated improvement in their hemoglobin level compared with 35.3% of patients in the placebo group.

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Figure 1. Proportions of patients (Pts) with or without anemia at baseline who had normal hemoglobin (Hgb) levels at week 24.

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Among all patients, statistically significant improvements in hemoglobin levels were observed for both ASAS20 responders and nonresponders treated with infliximab compared with placebo (Figure 2). Furthermore, among ASAS20 responders who had anemia at baseline, the median percent of increase in hemoglobin levels was significantly greater in the infliximab group than in the placebo group (20.80 versus 4.69; P = 0.008).

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Figure 2. Median percent change in hemoglobin level from baseline to week 24 for all patients and those with anemia at baseline. Lines indicate medians and boxes indicate interquartile ranges (IQRs). ASAS 20 = 20% improvement in the Assessment of SpondyloArthritis International Society criteria; ∗ = median (IQR) 4.69 (0.00, 4.76).

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Improvement in hemoglobin levels was significantly associated with improvements in physical function (β = −0.4414, P < 0.0001) and fatigue (β = −0.4296, P = 0.0076) (Table 2). Improvement in disease activity (β = 0.5838, P < 0.0001) and shorter disease duration (β = 0.0277, P = 0.0393) were also associated with improvement in physical function. Improvement in morning stiffness was significantly associated with improvement in fatigue (β = 0.5251, P < 0.0001).

Table 2. Association of improvements in physical function (BASFI score) and fatigue with improvement in hemoglobin*
 Association with physical functionAssociation with fatigue
βPβP
  • *

    BASDAI = Bath Ankylosing Spondylitis Disease Activity Index. See Table 1 for additional definitions.

  • r2 = 0.589 (n = 232).

  • r2 = 0.408 (n = 232).

Age, years−0.00720.53940.02270.2338
Sex−0.26440.30520.60740.1533
Disease duration, years0.02770.03930.01800.4109
Change in hemoglobin level−0.4414< 0.0001−0.42960.0076
IL-6 level0.01700.3165−0.00770.7810
CRP level−0.12810.09270.02560.8358
Change in BASDAI score0.5838< 0.0001
Change in morning stiffness0.5251< 0.0001

Effects of infliximab on the associations of baseline levels of CRP and IL-6 with hemoglobin levels at week 24

Among all patients in the infliximab group, those with baseline levels of CRP >0.5 mg/dl or IL-6 >7.46 pg/ml had significant improvements in hemoglobin level at week 24 when compared with patients who had baseline levels of CRP ≤0.5 mg/dl or IL-6 ≤7.46 pg/ml, respectively (Table 3). A similar pattern was observed for patients who had anemia at baseline. For all patients in the placebo group, there was no significant difference between the median changes in hemoglobin levels from baseline to week 24 for patients with baseline CRP levels >0.5 mg/dl and those with CRP levels ≤0.5 mg/dl. However, hemoglobin levels decreased significantly more in patients with baseline IL-6 levels >7.46 pg/ml than in patients with baseline IL-6 levels ≤7.46 pg/ml.

Table 3. Changes in hemoglobin level from baseline to week 24 stratified by CRP and IL-6 levels at baseline*
PatientsBaseline CRP levelBaseline IL-6 level
≤0.5 mg/dl>0.5 mg/dlP≤7.46 pg/ml>7.46 pg/mlP
  • *

    CRP = C-reactive protein; IL-6 = interleukin-6; IQR = interquartile range.

All      
 Placebo, n1256 3425 
  Median (IQR)−0.05 (−0.60, 0.60)−0.30 (−0.80, 0.20)0.1664−0.05 (−0.60, 0.40)−0.60 (−1.00, −0.10)0.0132
 Infliximab, n39149 8294 
  Median (IQR)−0.10 (−0.40, 0.40)0.90 (0.20, 1.60)< 0.00010.20 (−0.30, 0.80)1.30 (0.40, 2.00)< 0.0001
With anemia at baseline      
 Placebo, n29 27 
  Median (IQR)0.80 (0.60, 1.00)0.00 (−0.80, 0.70)0.24970.80 (0.60, 1.00)−0.60 (−1.00, 0.60)0.1020
 Infliximab, n532 1222 
  Median (IQR)−0.10 (−1.00, 0.90)2.20 (1.05, 2.65)0.00180.70 (−0.10, 1.05)2.45 (2.00, 2.80)< 0.0001

Among all patients, the probability of achieving an improvement in hemoglobin levels following treatment with infliximab was higher for patients with baseline levels of CRP >0.5 mg/dl or IL-6 >7.46 pg/ml than for those with baseline levels of CRP ≤0.5 mg/dl (OR 5.05, 95% CI 2.40–10.70) or IL-6 ≤7.46 pg/ml (OR 3.30, 95% CI 1.68–6.48), respectively. This relationship was also observed for CRP levels among patients with anemia at baseline (OR 14.50, 95% CI 1.69–124). For IL-6, there was a strong association between baseline IL-6 levels >7.46 pg/ml and improvement in hemoglobin levels, although this was not statistically significant (OR 5.00, 95% CI 0.76–32.90).

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. Acknowledgements
  10. REFERENCES

In the present study, over two-thirds of patients who had anemia at baseline and received infliximab had an improvement to normal levels of hemoglobin, suggesting that infliximab may have a beneficial effect on anemia, in addition to improving the signs and symptoms of AS. Studies exploring anemia in patients with AS are limited, and its clinical significance is yet to be fully understood. In this post hoc analysis of the ASSERT study, nearly 20% of patients had anemia at baseline. This is noteworthy because, to our knowledge, this is the largest analysis of anemia in patients with AS, and comprehensive studies on the prevalence of this comorbidity in patients with AS have not been conducted. However, because this analysis was limited to patients with AS who fulfilled the inclusion criteria for the ASSERT study, the prevalence of anemia among all patients with AS may differ.

The results of this analysis showed that treatment with infliximab led to improvements in hemoglobin levels and often to resolution of anemia. Furthermore, among patients who had normal hemoglobin levels at baseline, nearly all patients in the infliximab group maintained normal hemoglobin levels through week 24. Patients treated with infliximab also had significant improvements in fatigue VAS scores and BASFI scores compared with those who received placebo. Whereas improvements in fatigue and physical function would be expected with control of disease activity, we found that improvement in hemoglobin level was significantly associated with improvement in physical function and improvement in fatigue, independent of improvement in disease activity (BASDAI score or morning stiffness, respectively). This suggests that improvement in hemoglobin levels in patients with AS may be clinically relevant.

This study is limited primarily as a result of its retrospective design. This was a post hoc analysis of the ASSERT study, which was not specifically designed to evaluate anemia in patients with AS. Additionally, because we did not collect data on ferritin levels or mean corpuscular volume, the specific cause of anemia in these patients could not be determined from the collected assessments, and anemia may have resulted from factors other than inflammation. Of note, however, elevated levels of CRP (>0.5 mg/dl) or IL-6 (>7.46 pg/ml) at baseline were associated with improvement in hemoglobin levels, suggesting that the positive effect of infliximab on anemia is due to a systemic antiinflammatory effect. This may also indicate that the beneficial effect of infliximab is predominantly on anemia of chronic disease (inflammation) through reduced systemic inflammation, rather than on anemia of other causes, e.g., through the decreased use of NSAIDs as a result of infliximab treatment. More specifically, we hypothesize that a reduction in IL-6 levels, through inhibition of TNF after treatment with infliximab, may result in a reduction in hepcidin levels and alleviation of anemia. However, further research is needed to fully evaluate any relationship between infliximab treatment and levels of IL-6 and hepcidin.

Although chronic inflammation may be an important cause of anemia in these patients, the long-term use of NSAIDs, which is rather common in patients with AS, can lead to blood loss in the gastrointestinal tract (12). Therefore, because treatment with infliximab has been shown to reduce the need for NSAIDs among patients with AS (16), some of the improvement in hemoglobin levels in the infliximab group could also be attributable to a reduction in NSAID dose. However, because patients were asked to keep the use of NSAIDs stable during this portion of the trial, this effect was probably small in the present analysis.

Another potential cause of anemia is infection. In the ASSERT population, 27 (36%) of 75 patients in the placebo group and 86 (43%) of 202 patients in the infliximab group had ≥1 infection through week 24; however, infections were generally mild (e.g., upper respiratory tract infection and pharyngitis) (13). Only 2 patients reported a serious infection (both in the infliximab group). Therefore, the effect of infections on anemia in this patient population was likely minimal.

Finally, the 24-week study period was relatively short, and long-term studies are needed to fully understand the nature of anemia in patients with AS. The results presented here should not be construed as advocating anti-TNFα therapy as a primary treatment for anemia in patients with AS. We suggest, rather, that anemia in these patients be evaluated following conventional guidelines, and that improvement of hemoglobin levels may be a beneficial secondary effect in patients who are candidates for infliximab therapy.

This study is especially important given the limited data available on anemia in patients with AS, as well as the potential effects of anti-TNFα treatment on the pathophysiology of anemia in these patients. The results from this post hoc analysis of a large, placebo-controlled trial suggest that improvement of anemia following treatment with infliximab contributes to improvements in physical function and quality of life in patients with AS, even after adjusting for disease activity.

AUTHOR CONTRIBUTIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. Acknowledgements
  10. REFERENCES

All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be submitted for publication. 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 conception and design. Braun, van der Heijde, Doyle, Han, Deodhar, Inman, de Vlam, Burmester, Van denBosch, Xu, Visvanathan, Rahman.

Acquisition of data. Braun, van der Heijde, Doyle, Han, Deodhar, Inman, de Vlam, Burmester, Van denBosch, Xu, Visvanathan, Rahman.

Analysis and interpretation of data. Braun, van der Heijde, Doyle, Han, Deodhar, Inman, de Vlam, Burmester, Van denBosch, Xu, Visvanathan, Rahman.

ROLE OF THE STUDY SPONSOR

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. Acknowledgements
  10. REFERENCES

The conduct of the ASSERT study was managed by a steering committee consisting of Jürgen Braun, Désirée van der Heijde, and Paul Williamson. This committee designed the study with input from the Centocor clinical trial team. Data were collected by the study investigators and, for this post hoc analysis, the data were analyzed by authors Chenglong Han and Stephen Xu, who are Centocor employees. The data were interpreted by all authors, including Centocor employees. All authors reviewed the manuscript during its development, agreed to submit the manuscript, and approved the content of the final manuscript prior to submission.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. Acknowledgements
  10. REFERENCES

The authors thank Rebecca E. Clemente, PhD, and Robert Achenbach of Centocor for editorial support.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. Acknowledgements
  10. REFERENCES
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