- Email: [email protected]
Bronchiolitis obliterans syndrome is not specific for bronchiolitis obliterans in pediatric lung transplant
Author's Accepted Manuscript
Bronchiolitis Obliterans Syndrome Is Not Specific For Bronchiolitis Obliterans In Pediatric Lung Transplant Christopher Towe MD, A. Chester Ogborn MD, Thomas Ferkol MD, Stuart Sweet MD, PhD, Charles Huddleston MD, Frances White MD, Albert Faro MD
http://www.jhltonline.org
PII: DOI: Reference:
S1053-2498(14)01425-9 http://dx.doi.org/10.1016/j.healun.2014.10.004 HEALUN5894
To appear in:
J Heart Lung Transplant
Cite this article as: Christopher Towe MD, A. Chester Ogborn MD, Thomas Ferkol MD, Stuart Sweet MD, PhD, Charles Huddleston MD, Frances White MD, Albert Faro MD, Bronchiolitis Obliterans Syndrome Is Not Specific For Bronchiolitis Obliterans In Pediatric Lung Transplant, J Heart Lung Transplant, http://dx.doi.org/10.1016/j. healun.2014.10.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Title:
BRONCHIOLITIS OBLITERANS SYNDROME IS NOT SPECIFIC FOR BRONCHIOLITIS OBLITERANS IN PEDIATRIC LUNG TRANSPLANT
Authors:
Christopher Towe MD1, A. Chester Ogborn MD2, Thomas Ferkol MD3, Stuart Sweet MD, PhD3, Charles Huddleston MD4, Frances White MD3, Albert Faro MD3
Affiliations: OH
1. Cincinnati Children’s Hospital Medical Center, Cincinnati, 2. Scott & White Hospital, Temple, TX 3. Washington University School of Medicine, St. Louis, MO 4. St. Louis University, St. Louis, MO
Corresponding Author:
Albert Faro 660 S. Euclid Ave. #8116 St Louis, MO 63110 Phone: (314) 454-2707 Fax: (314) 454-2515 [email protected]
Running Title:
BOS is not Specific for BO
Key Words:
Bronchiolitis Obliterans Syndrome, Bronchiolitis Obliterans, Pediatric, Lung Transplant
Grant Support
CT: T32 - HL007873-15
Word Count:
2483
1
Abstract Background Bronchiolitis obliterans is the leading cause of mortality beyond the first year after pediatric lung transplant, but often requires the performance of an open lung biopsy for diagnosis. Bronchiolitis obliterans syndrome is a clinical diagnosis based on spirometric data that is the accepted standard for staging chronic allograft dysfunction. Methods We determined the sensitivity, specificity, positive and negative predictive values of bronchiolitis obliterans syndrome for predicting bronchiolitis obliterans in children. A chart review was conducted on the 139 open lung biopsies and 43 lung explants performed at our center from 1990 through June 2010 on pediatric lung transplant recipients. Results were excluded from analysis if insufficient data existed to calculate a stable bronchiolitis obliterans syndrome stage prior to biopsy/explant. Results 67 open lung biopsies and 31 lung explants met criteria for inclusion in the study. The sensitivity, specificity, positive predictive value, negative predictive value of BOS for predicting BO was 91.0%, 25.8%, 72.6%, and 57.1% respectively. Conclusions We found that early declines in lung function are sensitive but not specific for bronchiolitis obliterans. The low specificity for bronchiolitis obliterans syndrome to identify bronchiolitis obliterans illustrates the challenge facing clinicians in determining the etiology of pulmonary decline following lung transplant.
2
Introduction Lung transplantation may be the only opportunity for children with progressive or end-stage pulmonary disease to improve their quality of life and regain some degree of normal lung function. In contrast to other organ transplants, the long-term survival following lung transplantation is relatively poor with 5-year survival rates approximating only 50%1,2. The most common long-term complication is bronchiolitis obliterans (BO). More than 50% of lung transplant recipients are diagnosed with BO by 5-years after transplantation and over 40% of deaths occurring more than 1-year after transplantation are the direct result of BO1. The diagnosis of BO requires careful histological examination of the involved airways. Early in BO, few pathologic changes are evident. Classic histological findings for BO begin to appear as the disease progresses, including peri- and endobronchial lymphocytic infiltration, fibromyxoid deposits, and ultimately fibrous replacement of the airways3. Destruction and obliteration of the airways may be profound, leaving the affected bronchioles obscured by fibrosis and virtually unrecognizable. Because of the heterogeneous distribution of BO, transbronchial biopsy often fails to establish the diagnosis4, with sensitivities less than 20%5,6. Open lung biopsy (OLB) remains the accepted gold standard for the diagnosis of BO. Because of these diagnostic limitations, a clinical description, bronchiolitis obliterans syndrome (BOS) was created to characterize the unexplained development and progression of airflow obstruction in a lung transplant recipient7. The criteria for BOS is primarily defined by a persistent decline in forced expiratory volume in one second (FEV1) greater than 20% from baseline values, taken from the average of two best measures at least 3 weeks apart. Additionally, infection or acute graft rejection, concurrent processes that can cause declining lung function in a lung transplant recipient, must be excluded. Although BOS is used as a clinical marker for BO in lung transplant recipients, little direct evidence exists that validates this association. Autopsy data and pathologic examination of explanted lungs of retransplant recipients following BOS have inconsistently revealed BO, and in some cases demonstrated other pathologic changes, such as interstitial fibrosis or invasive
3
fungal disease8,9. Additionally, BO severity has not necessarily correlated with severity of BOS score9,10. Furthermore, BOS criteria must be modified for use in the pediatric population. In pediatric subjects, since the patient is still growing, raw values for pulmonary function, including FEV1, are dynamic. The baseline lung function is adjusted based on the patient’s height, age, race and gender, with each measurement expressed as a percentage of predicted value. Later reduction from baseline is expressed in terms of percentage decline relative to the baseline predicted value. Since the use of BOS as a clinical marker for BO has not been established, this modification to the definition of BOS has been difficult to validate. This retrospective study is the first to attempt to correlate the pulmonary function decline with the histopathologic findings seen in pediatric lung transplant recipients. We tested the hypothesis that the current BOS definition would accurately predict the histopathologic diagnosis of BO, and we determined the sensitivity and specificity of BOS classification for BO diagnosed by tissue histopathology.
4
Materials and Methods Study design: A retrospective cohort analysis of all pediatric lung transplant recipients 5 years of age or older who underwent OLB or lung explantation as part of a retransplant procedure was performed to assess the sensitivity and specificity of pulmonary function testing to detect BO. Records of pulmonary function testing, pathology and microbiologic data were reviewed. The Washington University School of Medicine Human Research Protection Office approved the study protocol. Clinical data: Spirometry was routinely performed at our center at least weekly following hospital discharge during the first three months following transplantation, then quarterly for the next nine months, and at all subsequent follow-up evaluations or whenever clinically indicated. All measurements were performed at the St Louis Children’s Hospital Pulmonary Function Laboratory according to American Thoracic Society Guidelines11, and predicted values were calculated using standards from Wang and Dockery12. The two best values for FEV1, measured at least three weeks apart, were averaged to calculate the baseline FEV1. In contrast to the adult scoring system, all values were expressed as percentage of predicted volume to account for the lung growth in the pediatric populations. OLB were obtained based on clinical suspicion of BO; the institutional practice was to confirm BO histopathologically by OLB if not already detected by transbronchial biopsy. OLB and explant results were excluded from analysis if (1) inadequate spirometry data was available to determine a stable BOS stage, (2) the patient was unable to perform spirometry, (3) OLB or explant was performed within the first three months of the lung transplant, (4) the patient was over 18 years of age at the time of transplant, (5) OLB specimen was inadequate for analysis, or (6) the explant followed an OLB. A priori, patients with evidence of significant stenotic anastamoses, pleural disease, or diaphragmatic dysfunction were going to be excluded, but no patients met these criteria. The spirometric data immediately preceding a patient’s OLB or explant was used to determine whether the patient met criteria for BOS. The patient was classified as having BOS if the average of these previous two FEV1 percent predicted values, measured at least
5
three weeks apart, were reduced more than 20 percent from the patient’s calculated baseline. Histopathological evaluation: Histopathology reports for both OLB and explants were reviewed and considered positive if a BO score was given according to the International Society for Heart and Lung Transplantation Working Formulation. Patients were considered to have acute rejection if tissue from an OLB or explant was scored grade A2 or greater, i.e., mild rejection represented by perivascular mononuclear infiltrates, or higher on histopathology reports13. Additional diagnoses were made according to standard pathology practice. Statistical analysis: Results were reported as mean + standard deviation. Significance tests were one-way analysis of variance for continuous variable and Pearson Chi Square analysis for binomial variables. Kaplan-Meier survival analysis was performed to determine freedom from BO. Sensitivity, specificity, positive predictive value and negative predictive value were calculated for the ability of BOS to detect BO on OLB or explant. Calculations were performed in SPSS version 9.2.
6
Results Between July 1990 and June 2010, a total of 370 pediatric lung transplants were performed by the Washington University Pediatric Lung Transplantation Center at St Louis Children’s Hospital; 170 of these patients developed BO, and the Kaplan-Meier freedom from BO was 62% at three years and 49% at five years. In patients who had undergone lung transplant, 139 OLB were performed and 43 lungs were explanted as part of a second lung transplant. 72 OLB and 12 explants were excluded from analysis, as detailed in Figure 1, resulting in lung tissues from 67 subjects who underwent OLB and 31 subjects who received a second lung transplantation undergoing further analysis. The clinical characteristics of the subjects analyzed, grouped by those who underwent OLB and explant for a second lung transplant are detailed in Table 1. There was no significant difference between the two groups in pre-transplant characteristics such as age at transplant, gender and underlying diagnosis. There was also no difference in posttransplant peak FEV1. However, as might be expected, the patients who underwent second transplantation were significantly more removed from transplant (p = 0.007) and their last pulmonary function tests (p < 0.001). They also had greater declines in their FEV1 (p<0.001), were more likely to have BOS (p = 0.006), and were more likely to have BO (p = 0.025). Table 2 outlines the clinical characteristics of the subjects separated by the presence of BOS. There were no significant differences in the two groups except that patients without BOS had less of a decline in FEV1 (p < 0.001), were less likely to have BO (p = 0.027) and were more likely to have an open lung biopsy instead of an explant (p = 0.006). Overall, including open lung biopsies and explants, the sensitivity for BOS diagnosing BO was 91.0% (84.2 – 97.9) and the specificity was 25.8% (10.4 – 41.2). The positive and negative predictive values were 72.6% (63.1 – 82.2) and 57.1% (31.2 – 83.1), respectively. The positive likelihood ratio was 1.23 (0.984 – 1.53) which is not significantly different than 1. The negative likelihood ratio was 0.347 (0.132 – 0.915) (Table 3). The numbers were similar when adjusted for 1-year conditional survival and when only data concerning open lung
7
biopsies is considered. However, in these cases neither the positive nor negative likelihood ratios were significantly different than 1. Explants as a stand-alone group were excluded from this analysis because all of these individuals had BOS. Table 4 shows the pathologic diagnoses of the specimens that did not demonstrate histologic evidence of BO. Many diverse disease processes were identified including immune mediated processes, nonspecific inflammatory processes, interstitial fibrosis, infections and malignancy.
8
Discussion Bronchiolitis obliterans is the most significant contributor to morbidity and mortality after the first year post-lung transplantation. BOS criteria were developed and widely applied as a clinical surrogate for histopathologic diagnosis to aid in clinical decision-making. However, few studies have been performed to validate this scoring system, and none in pediatric recipients. We retrospectively analyzed spirometric and histopathologic data from pediatric bilateral lung transplant recipients and determined that BOS is sensitive, but not specific for the diagnosis of BO. The overall sensitivity of BOS in our study was 91.0%, which suggests that spirometry is a fair screening test for BO. However, the low specificity and positive likelihood ratio indicated that the use of BOS as a clinical surrogate for BO without other confirmatory testing is problematic. Overestimating BO could result in excessive augmentation of immunosuppression, which could have serious consequences including exacerbation of undetected infection. Previously unrecognized invasive fungal disease was found on explant in one study, which may have accounted for the decline in lung function14. Patients receiving overly aggressive immunosuppression are also at increased risk for additional side effects, such as post-transplant lymphoproliferative disorders. When faced with the possibility of BO, our data supports our institution’s current clinical practice of obtaining additional evidence from imaging studies and tissue histopathology when patients present with significant lung function decline. After obtaining chest imaging, including computed x-ray tomography, our standard of care is to perform flexible bronchoscopy with bronchoalveolar lavage and transbronchial biopsies. If those results are inconclusive, OLB is obtained before making significant changes in therapy. The false positives in our study may also reflect the limitation of other diagnostic techniques to identify additional etiologies of obstruction, such as viral infections or gastroesophageal reflux disease in the pathogenesis of BO. Data addressing antibodymediated rejection were not available. As newer molecular techniques become available and accurate biomarkers are identified, better identification of pathology could improve
9
sensitivity and specificity of BOS scoring. The use of additional measures such as enhanced imaging techniques was not addressed, which could further aid in discriminating which patients are most at risk for having BO. In the past few years, it has become increasingly recognized that some lung transplant recipients develop restrictive changes on pulmonary function testing instead of obstructive changes. This syndrome has been named restrictive allograft syndrome (RAS)15. As such, the broader term chronic lung allograft dysfunction (CLAD) is becoming more accepted with two primary subtypes: BOS and RAS. Patients who develop RAS also have a marked decline in FEV1 and would have been classified as BOS in the current study. This may account for some of the false positive as the pathologic correlates of RAS have yet to be fully described and are not currently in use clinically. Once the pathologic features have been described, distinguishing the specific CLAD phenotypes will be paramount in guiding appropriate management. As disconcerting as the poor positive likelihood ratio of BOS for BO is, in patients over 1 year post-transplant or when explants are excluded from analysis, neither the positive nor negative likelihood ratios are significantly different than 1. This indicates that in certain clinical scenarios, not having BOS does not significantly protect you from having BO. One reason for this finding may be the lower average peak FEV1 achieved by those patients who did not meet criteria for the diagnosis of BOS, but clinically warranted an OLB versus those patients meeting criteria for BOS. While this finding only trended toward statistical significance in our study, it has been previously reported that the likelihood of being diagnosed with BOS is dependent on the maximum FEV1 achieved post-transplant16. Therefore, perhaps a modification of the definition for BOS should be considered so that a certain minimum post-transplant FEV1 should be obtained before BOS scores are used in clinical decision making. Unfortunately, our data set is too small to test this hypothesis. Obtaining an OLB from a lung transplant recipient is not without risk, and the complication rate was previously reported by our institution17. In that study, which included many of the current patients, there were no mortalities directly attributed to the OLB. There
10
was an 11% (11/103) “major” complication rate, including postoperative respiratory failure (6), acute renal failure (2), postoperative hemorrhage requiring re-exploration (2) and newonset supplemental oxygen dependence. There was 21% (22/103) “minor” complication rate mostly consisting of postoperative pneumothorax requiring thoracostomy tube insertion (12) or presentation after hospital discharge for evaluation of postoperative pain (6). The current study was limited by the paucity of negative controls for the OLB, since patients do not undergo OLB without clinical suspicion. Additionally, almost half (n = 84) of our samples had to be excluded from analysis. Some were excluded for clear reasons such as inadequate tissue biopsy sample or they were collected too soon following transplantation for the development of BOS or BO. Many were excluded because the patients were either too young to perform spirometry (n = 27) or too old to be considered pediatric patients (n = 10). A large group (n = 26) was excluded because they had inadequate spirometry data to meet our strict definition of BOS. Many of these patients presented with precipitous drops in lung function, or even acute respiratory failure, and therefore did not have the requisite spirometric data to meet the strict definition of BOS. BOS criteria must be modified for use in the pediatric population. In pediatric subjects, since the patient is still growing, absolute values for pulmonary function, including FEV1, change over time. The baseline lung function is adjusted based on the patient’s height, age, race and gender, with each measurement expressed as a percentage of predicted value. Later decline from baseline is expressed in terms of percentage decline relative to the predicted absolute baseline value. This study does not support the use of BOS to diagnose BO, and so cannot be used to comment on the use of percentage of predicted values instead of absolute FEV1 measures. In summary, BOS in pediatric lung transplant recipients represents a broader array of potential histologic diagnoses than BO alone, reflecting the limitations of non-invasive surrogate measures available to clinicians. BOS should not be used as a substitute diagnosis for BO, or more importantly as a reason to significantly augment
11
immunosuppression, if other diagnostic tools such as histopathological confirmation are available.
Acknowledgements The authors wish to acknowledge Dr. Peter Michelson for his assistance editing the final manuscript. Christopher Towe was supported by the Institutional Training Grant Pediatric cardiovascular and pulmonary research training program (T32 HL007873-15).
Conflicts of Interest The authors have no financial conflicts of interest.
12
References 1. Benden C, Edwards L, Kucheryavaya AY, et al. The Registry of the International Society for Heart and Lung Transplantation: Sixteenth official pediatric lung and heart-lung transplantation report-2013; Focus theme: Age. J Heart Lung Transplant 2013; 32(10): 989-997. 2. Yusen RD, Christie JD, Edwards LB, et al. The Registry of the International Society for Heart and Lung Transplantation: Thirtieth adult lung and heart-lung transplantation report-2013; Focus theme: Age. J Heart Lung Transplant 2013; 32(10): 965-978. 3. Cooper JD, Billingham M, Egan T, et al. A working formulation for the standardization of nomenclature and for clinical staging of chronic dysfunction in lung allografts. J Heart Lung Transplant 1993; 12(5): 713-716. 4. Cagle PT, Brown RW, Frost A, Kellar C, Yousem SA. Diagnosis of chronic lung transplant rejection by transbronchial biopsy. Mod Pathol 1995; 8(2): 137-142. 5. Chamberlain D, Maurer J, Chaparro C, Idolor L. Evaluation of transbronchial lung biopsy specimens in the diagnosis of bronchiolitis obliterans after lung transplantation. J Heart Lung Transplant 1994; 13(6): 963-971. 6. Kramer MR, Stoehr C, Whang JL, et al. The diagnosis of obliterative bronchiolitis after heart-lung and lung transplantation: low yield of transbronchial lung biopsy. J Heart Lung Transplant 1993; 12(4): 675-681. 7. Estenne M, Maurer JR, Boehler A, et al. Bronchiolitis obliterans syndrome 2001: an update of the diagnostic criteria. J Heart Lung Transplant 2002; 21(3): 297-310. 8. Burke CM, Theodore J, Dawkins KD, et al. Post-transplant obliterative bronchiolitis and other late lung sequelae in human heart-lung transplantation. Chest 1984; 86(6): 824-829.
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9. Martinu T, Howell DN, Davis RD, Steele MP, Palmer SM. Pathologic correlates of bronchiolitis obliterans syndrome in pulmonary retransplant recipients. Chest 2006; 129(4):1016-1023. 10. Kaditis AG, Phadke S, Dickman P, Webber S, Kurland G, Michaels MG. Mortality after pediatric lung transplantation: autopsies vs. clinical impression. Pediatric Pulmonol 2004; 37(5):413-418. 11. Miller MR, Hankinson J, Brusasco V, et al. Standardisation of spirometry. Eur Respir J 2005; 26(2): 319-338. 12. Wang X, Dockery DW, et al. Pulmonary Function Between 6 and 18 Years of Age. Ped Pulm 1993; 15: 75-88. 13. Stewart S, Fishbein MC, Snell GI, et al. Revision of the 1996 working formulation for the standardization of nomenclature in the diagnosis of lung rejection. J Heart Lung Transplant 2007; 26(12):1229-1242. 14. Martinu T, Howell DN, Davis RD, Steele MP, Palmer SM. Pathologic correlates of bronchiolitis obliterans syndrome in pulmonary retransplant recipients. Chest 2006; 129(4):1016-1023. 15. Sato M, Waddell TK, Wagnetz U, et al. Restrictive allograft syndrome (RAS): A novel form of chronic lung allograft dysfunction. J Heart Lung Transplant 2011; 30: 735742. 16. Burton CM, Iversen M, Mortensen J, et al. Post-transplant baseline FEV1 and the development of bronchiolitis obliterans syndrome: an important confounder? J Heart Lung Transplant 2007; 26(11): 1127-1134. 17. Choong CK, Haddad FJ, Huddleston CB, et al. Role of open lung biopsy in lung transplant recipients in a single children’s hospital: A 13-year experience. J Thorac Cardiovasc Surg 2006; 131: 204-208.
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Figure Legends Figure 1 – After the 370 pediatric lung transplants, 139 open lung biopsies (OLB) and 43 lung explants were performed. 72 OLB and 12 explants were excluded for the reasons listed leaving 67 OLB and 31 explants which underwent further analysis.
15
Table Legends Table 1 – Patient characteristics at the time of pathologic diagnosis for the group overall, those with open lung biopsies and those with explants. Results reported as either percent or mean ± standard deviation.
16
Table 2 – Patient characteristics at the time of pathologic diagnosis for those with and without bronchiolitis obliterans syndrome. Results reported as mean ± standard deviation.
17
Table 3 - Sensitivity, Specificity, Positive Predictive Values, Negative Predictive Values, Positive Likelihood Ratios and Negative Likelihood Ratios of bronchiolitis obliterans syndrome for the diagnosis of bronchiolitis obliterans for the group overall, for those patients with 1 year conditional survival post-transplant and for those patients who underwent open lung biopsy. Results reported as calculated value (95% confidence interval).
18
Table 4 – List of pathologic diagnoses on open lung biopsy or explant other than bronchiolitis obliterans. Number in parenthesis is incidence if greater than 1.
19
Bronchiolitis Obliterans Syndrome Is Not Specific For Bronchiolitis Obliterans In Pediatric Lung Transplant Christopher Towe MD, A. Chester Ogborn MD, Thomas Ferkol MD, Stuart Sweet MD, PhD, Charles Huddleston MD, Frances White MD, Albert Faro MD
http://www.jhltonline.org
PII: DOI: Reference:
S1053-2498(14)01425-9 http://dx.doi.org/10.1016/j.healun.2014.10.004 HEALUN5894
To appear in:
J Heart Lung Transplant
Cite this article as: Christopher Towe MD, A. Chester Ogborn MD, Thomas Ferkol MD, Stuart Sweet MD, PhD, Charles Huddleston MD, Frances White MD, Albert Faro MD, Bronchiolitis Obliterans Syndrome Is Not Specific For Bronchiolitis Obliterans In Pediatric Lung Transplant, J Heart Lung Transplant, http://dx.doi.org/10.1016/j. healun.2014.10.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Title:
BRONCHIOLITIS OBLITERANS SYNDROME IS NOT SPECIFIC FOR BRONCHIOLITIS OBLITERANS IN PEDIATRIC LUNG TRANSPLANT
Authors:
Christopher Towe MD1, A. Chester Ogborn MD2, Thomas Ferkol MD3, Stuart Sweet MD, PhD3, Charles Huddleston MD4, Frances White MD3, Albert Faro MD3
Affiliations: OH
1. Cincinnati Children’s Hospital Medical Center, Cincinnati, 2. Scott & White Hospital, Temple, TX 3. Washington University School of Medicine, St. Louis, MO 4. St. Louis University, St. Louis, MO
Corresponding Author:
Albert Faro 660 S. Euclid Ave. #8116 St Louis, MO 63110 Phone: (314) 454-2707 Fax: (314) 454-2515 [email protected]
Running Title:
BOS is not Specific for BO
Key Words:
Bronchiolitis Obliterans Syndrome, Bronchiolitis Obliterans, Pediatric, Lung Transplant
Grant Support
CT: T32 - HL007873-15
Word Count:
2483
1
Abstract Background Bronchiolitis obliterans is the leading cause of mortality beyond the first year after pediatric lung transplant, but often requires the performance of an open lung biopsy for diagnosis. Bronchiolitis obliterans syndrome is a clinical diagnosis based on spirometric data that is the accepted standard for staging chronic allograft dysfunction. Methods We determined the sensitivity, specificity, positive and negative predictive values of bronchiolitis obliterans syndrome for predicting bronchiolitis obliterans in children. A chart review was conducted on the 139 open lung biopsies and 43 lung explants performed at our center from 1990 through June 2010 on pediatric lung transplant recipients. Results were excluded from analysis if insufficient data existed to calculate a stable bronchiolitis obliterans syndrome stage prior to biopsy/explant. Results 67 open lung biopsies and 31 lung explants met criteria for inclusion in the study. The sensitivity, specificity, positive predictive value, negative predictive value of BOS for predicting BO was 91.0%, 25.8%, 72.6%, and 57.1% respectively. Conclusions We found that early declines in lung function are sensitive but not specific for bronchiolitis obliterans. The low specificity for bronchiolitis obliterans syndrome to identify bronchiolitis obliterans illustrates the challenge facing clinicians in determining the etiology of pulmonary decline following lung transplant.
2
Introduction Lung transplantation may be the only opportunity for children with progressive or end-stage pulmonary disease to improve their quality of life and regain some degree of normal lung function. In contrast to other organ transplants, the long-term survival following lung transplantation is relatively poor with 5-year survival rates approximating only 50%1,2. The most common long-term complication is bronchiolitis obliterans (BO). More than 50% of lung transplant recipients are diagnosed with BO by 5-years after transplantation and over 40% of deaths occurring more than 1-year after transplantation are the direct result of BO1. The diagnosis of BO requires careful histological examination of the involved airways. Early in BO, few pathologic changes are evident. Classic histological findings for BO begin to appear as the disease progresses, including peri- and endobronchial lymphocytic infiltration, fibromyxoid deposits, and ultimately fibrous replacement of the airways3. Destruction and obliteration of the airways may be profound, leaving the affected bronchioles obscured by fibrosis and virtually unrecognizable. Because of the heterogeneous distribution of BO, transbronchial biopsy often fails to establish the diagnosis4, with sensitivities less than 20%5,6. Open lung biopsy (OLB) remains the accepted gold standard for the diagnosis of BO. Because of these diagnostic limitations, a clinical description, bronchiolitis obliterans syndrome (BOS) was created to characterize the unexplained development and progression of airflow obstruction in a lung transplant recipient7. The criteria for BOS is primarily defined by a persistent decline in forced expiratory volume in one second (FEV1) greater than 20% from baseline values, taken from the average of two best measures at least 3 weeks apart. Additionally, infection or acute graft rejection, concurrent processes that can cause declining lung function in a lung transplant recipient, must be excluded. Although BOS is used as a clinical marker for BO in lung transplant recipients, little direct evidence exists that validates this association. Autopsy data and pathologic examination of explanted lungs of retransplant recipients following BOS have inconsistently revealed BO, and in some cases demonstrated other pathologic changes, such as interstitial fibrosis or invasive
3
fungal disease8,9. Additionally, BO severity has not necessarily correlated with severity of BOS score9,10. Furthermore, BOS criteria must be modified for use in the pediatric population. In pediatric subjects, since the patient is still growing, raw values for pulmonary function, including FEV1, are dynamic. The baseline lung function is adjusted based on the patient’s height, age, race and gender, with each measurement expressed as a percentage of predicted value. Later reduction from baseline is expressed in terms of percentage decline relative to the baseline predicted value. Since the use of BOS as a clinical marker for BO has not been established, this modification to the definition of BOS has been difficult to validate. This retrospective study is the first to attempt to correlate the pulmonary function decline with the histopathologic findings seen in pediatric lung transplant recipients. We tested the hypothesis that the current BOS definition would accurately predict the histopathologic diagnosis of BO, and we determined the sensitivity and specificity of BOS classification for BO diagnosed by tissue histopathology.
4
Materials and Methods Study design: A retrospective cohort analysis of all pediatric lung transplant recipients 5 years of age or older who underwent OLB or lung explantation as part of a retransplant procedure was performed to assess the sensitivity and specificity of pulmonary function testing to detect BO. Records of pulmonary function testing, pathology and microbiologic data were reviewed. The Washington University School of Medicine Human Research Protection Office approved the study protocol. Clinical data: Spirometry was routinely performed at our center at least weekly following hospital discharge during the first three months following transplantation, then quarterly for the next nine months, and at all subsequent follow-up evaluations or whenever clinically indicated. All measurements were performed at the St Louis Children’s Hospital Pulmonary Function Laboratory according to American Thoracic Society Guidelines11, and predicted values were calculated using standards from Wang and Dockery12. The two best values for FEV1, measured at least three weeks apart, were averaged to calculate the baseline FEV1. In contrast to the adult scoring system, all values were expressed as percentage of predicted volume to account for the lung growth in the pediatric populations. OLB were obtained based on clinical suspicion of BO; the institutional practice was to confirm BO histopathologically by OLB if not already detected by transbronchial biopsy. OLB and explant results were excluded from analysis if (1) inadequate spirometry data was available to determine a stable BOS stage, (2) the patient was unable to perform spirometry, (3) OLB or explant was performed within the first three months of the lung transplant, (4) the patient was over 18 years of age at the time of transplant, (5) OLB specimen was inadequate for analysis, or (6) the explant followed an OLB. A priori, patients with evidence of significant stenotic anastamoses, pleural disease, or diaphragmatic dysfunction were going to be excluded, but no patients met these criteria. The spirometric data immediately preceding a patient’s OLB or explant was used to determine whether the patient met criteria for BOS. The patient was classified as having BOS if the average of these previous two FEV1 percent predicted values, measured at least
5
three weeks apart, were reduced more than 20 percent from the patient’s calculated baseline. Histopathological evaluation: Histopathology reports for both OLB and explants were reviewed and considered positive if a BO score was given according to the International Society for Heart and Lung Transplantation Working Formulation. Patients were considered to have acute rejection if tissue from an OLB or explant was scored grade A2 or greater, i.e., mild rejection represented by perivascular mononuclear infiltrates, or higher on histopathology reports13. Additional diagnoses were made according to standard pathology practice. Statistical analysis: Results were reported as mean + standard deviation. Significance tests were one-way analysis of variance for continuous variable and Pearson Chi Square analysis for binomial variables. Kaplan-Meier survival analysis was performed to determine freedom from BO. Sensitivity, specificity, positive predictive value and negative predictive value were calculated for the ability of BOS to detect BO on OLB or explant. Calculations were performed in SPSS version 9.2.
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Results Between July 1990 and June 2010, a total of 370 pediatric lung transplants were performed by the Washington University Pediatric Lung Transplantation Center at St Louis Children’s Hospital; 170 of these patients developed BO, and the Kaplan-Meier freedom from BO was 62% at three years and 49% at five years. In patients who had undergone lung transplant, 139 OLB were performed and 43 lungs were explanted as part of a second lung transplant. 72 OLB and 12 explants were excluded from analysis, as detailed in Figure 1, resulting in lung tissues from 67 subjects who underwent OLB and 31 subjects who received a second lung transplantation undergoing further analysis. The clinical characteristics of the subjects analyzed, grouped by those who underwent OLB and explant for a second lung transplant are detailed in Table 1. There was no significant difference between the two groups in pre-transplant characteristics such as age at transplant, gender and underlying diagnosis. There was also no difference in posttransplant peak FEV1. However, as might be expected, the patients who underwent second transplantation were significantly more removed from transplant (p = 0.007) and their last pulmonary function tests (p < 0.001). They also had greater declines in their FEV1 (p<0.001), were more likely to have BOS (p = 0.006), and were more likely to have BO (p = 0.025). Table 2 outlines the clinical characteristics of the subjects separated by the presence of BOS. There were no significant differences in the two groups except that patients without BOS had less of a decline in FEV1 (p < 0.001), were less likely to have BO (p = 0.027) and were more likely to have an open lung biopsy instead of an explant (p = 0.006). Overall, including open lung biopsies and explants, the sensitivity for BOS diagnosing BO was 91.0% (84.2 – 97.9) and the specificity was 25.8% (10.4 – 41.2). The positive and negative predictive values were 72.6% (63.1 – 82.2) and 57.1% (31.2 – 83.1), respectively. The positive likelihood ratio was 1.23 (0.984 – 1.53) which is not significantly different than 1. The negative likelihood ratio was 0.347 (0.132 – 0.915) (Table 3). The numbers were similar when adjusted for 1-year conditional survival and when only data concerning open lung
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biopsies is considered. However, in these cases neither the positive nor negative likelihood ratios were significantly different than 1. Explants as a stand-alone group were excluded from this analysis because all of these individuals had BOS. Table 4 shows the pathologic diagnoses of the specimens that did not demonstrate histologic evidence of BO. Many diverse disease processes were identified including immune mediated processes, nonspecific inflammatory processes, interstitial fibrosis, infections and malignancy.
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Discussion Bronchiolitis obliterans is the most significant contributor to morbidity and mortality after the first year post-lung transplantation. BOS criteria were developed and widely applied as a clinical surrogate for histopathologic diagnosis to aid in clinical decision-making. However, few studies have been performed to validate this scoring system, and none in pediatric recipients. We retrospectively analyzed spirometric and histopathologic data from pediatric bilateral lung transplant recipients and determined that BOS is sensitive, but not specific for the diagnosis of BO. The overall sensitivity of BOS in our study was 91.0%, which suggests that spirometry is a fair screening test for BO. However, the low specificity and positive likelihood ratio indicated that the use of BOS as a clinical surrogate for BO without other confirmatory testing is problematic. Overestimating BO could result in excessive augmentation of immunosuppression, which could have serious consequences including exacerbation of undetected infection. Previously unrecognized invasive fungal disease was found on explant in one study, which may have accounted for the decline in lung function14. Patients receiving overly aggressive immunosuppression are also at increased risk for additional side effects, such as post-transplant lymphoproliferative disorders. When faced with the possibility of BO, our data supports our institution’s current clinical practice of obtaining additional evidence from imaging studies and tissue histopathology when patients present with significant lung function decline. After obtaining chest imaging, including computed x-ray tomography, our standard of care is to perform flexible bronchoscopy with bronchoalveolar lavage and transbronchial biopsies. If those results are inconclusive, OLB is obtained before making significant changes in therapy. The false positives in our study may also reflect the limitation of other diagnostic techniques to identify additional etiologies of obstruction, such as viral infections or gastroesophageal reflux disease in the pathogenesis of BO. Data addressing antibodymediated rejection were not available. As newer molecular techniques become available and accurate biomarkers are identified, better identification of pathology could improve
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sensitivity and specificity of BOS scoring. The use of additional measures such as enhanced imaging techniques was not addressed, which could further aid in discriminating which patients are most at risk for having BO. In the past few years, it has become increasingly recognized that some lung transplant recipients develop restrictive changes on pulmonary function testing instead of obstructive changes. This syndrome has been named restrictive allograft syndrome (RAS)15. As such, the broader term chronic lung allograft dysfunction (CLAD) is becoming more accepted with two primary subtypes: BOS and RAS. Patients who develop RAS also have a marked decline in FEV1 and would have been classified as BOS in the current study. This may account for some of the false positive as the pathologic correlates of RAS have yet to be fully described and are not currently in use clinically. Once the pathologic features have been described, distinguishing the specific CLAD phenotypes will be paramount in guiding appropriate management. As disconcerting as the poor positive likelihood ratio of BOS for BO is, in patients over 1 year post-transplant or when explants are excluded from analysis, neither the positive nor negative likelihood ratios are significantly different than 1. This indicates that in certain clinical scenarios, not having BOS does not significantly protect you from having BO. One reason for this finding may be the lower average peak FEV1 achieved by those patients who did not meet criteria for the diagnosis of BOS, but clinically warranted an OLB versus those patients meeting criteria for BOS. While this finding only trended toward statistical significance in our study, it has been previously reported that the likelihood of being diagnosed with BOS is dependent on the maximum FEV1 achieved post-transplant16. Therefore, perhaps a modification of the definition for BOS should be considered so that a certain minimum post-transplant FEV1 should be obtained before BOS scores are used in clinical decision making. Unfortunately, our data set is too small to test this hypothesis. Obtaining an OLB from a lung transplant recipient is not without risk, and the complication rate was previously reported by our institution17. In that study, which included many of the current patients, there were no mortalities directly attributed to the OLB. There
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was an 11% (11/103) “major” complication rate, including postoperative respiratory failure (6), acute renal failure (2), postoperative hemorrhage requiring re-exploration (2) and newonset supplemental oxygen dependence. There was 21% (22/103) “minor” complication rate mostly consisting of postoperative pneumothorax requiring thoracostomy tube insertion (12) or presentation after hospital discharge for evaluation of postoperative pain (6). The current study was limited by the paucity of negative controls for the OLB, since patients do not undergo OLB without clinical suspicion. Additionally, almost half (n = 84) of our samples had to be excluded from analysis. Some were excluded for clear reasons such as inadequate tissue biopsy sample or they were collected too soon following transplantation for the development of BOS or BO. Many were excluded because the patients were either too young to perform spirometry (n = 27) or too old to be considered pediatric patients (n = 10). A large group (n = 26) was excluded because they had inadequate spirometry data to meet our strict definition of BOS. Many of these patients presented with precipitous drops in lung function, or even acute respiratory failure, and therefore did not have the requisite spirometric data to meet the strict definition of BOS. BOS criteria must be modified for use in the pediatric population. In pediatric subjects, since the patient is still growing, absolute values for pulmonary function, including FEV1, change over time. The baseline lung function is adjusted based on the patient’s height, age, race and gender, with each measurement expressed as a percentage of predicted value. Later decline from baseline is expressed in terms of percentage decline relative to the predicted absolute baseline value. This study does not support the use of BOS to diagnose BO, and so cannot be used to comment on the use of percentage of predicted values instead of absolute FEV1 measures. In summary, BOS in pediatric lung transplant recipients represents a broader array of potential histologic diagnoses than BO alone, reflecting the limitations of non-invasive surrogate measures available to clinicians. BOS should not be used as a substitute diagnosis for BO, or more importantly as a reason to significantly augment
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immunosuppression, if other diagnostic tools such as histopathological confirmation are available.
Acknowledgements The authors wish to acknowledge Dr. Peter Michelson for his assistance editing the final manuscript. Christopher Towe was supported by the Institutional Training Grant Pediatric cardiovascular and pulmonary research training program (T32 HL007873-15).
Conflicts of Interest The authors have no financial conflicts of interest.
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References 1. Benden C, Edwards L, Kucheryavaya AY, et al. The Registry of the International Society for Heart and Lung Transplantation: Sixteenth official pediatric lung and heart-lung transplantation report-2013; Focus theme: Age. J Heart Lung Transplant 2013; 32(10): 989-997. 2. Yusen RD, Christie JD, Edwards LB, et al. The Registry of the International Society for Heart and Lung Transplantation: Thirtieth adult lung and heart-lung transplantation report-2013; Focus theme: Age. J Heart Lung Transplant 2013; 32(10): 965-978. 3. Cooper JD, Billingham M, Egan T, et al. A working formulation for the standardization of nomenclature and for clinical staging of chronic dysfunction in lung allografts. J Heart Lung Transplant 1993; 12(5): 713-716. 4. Cagle PT, Brown RW, Frost A, Kellar C, Yousem SA. Diagnosis of chronic lung transplant rejection by transbronchial biopsy. Mod Pathol 1995; 8(2): 137-142. 5. Chamberlain D, Maurer J, Chaparro C, Idolor L. Evaluation of transbronchial lung biopsy specimens in the diagnosis of bronchiolitis obliterans after lung transplantation. J Heart Lung Transplant 1994; 13(6): 963-971. 6. Kramer MR, Stoehr C, Whang JL, et al. The diagnosis of obliterative bronchiolitis after heart-lung and lung transplantation: low yield of transbronchial lung biopsy. J Heart Lung Transplant 1993; 12(4): 675-681. 7. Estenne M, Maurer JR, Boehler A, et al. Bronchiolitis obliterans syndrome 2001: an update of the diagnostic criteria. J Heart Lung Transplant 2002; 21(3): 297-310. 8. Burke CM, Theodore J, Dawkins KD, et al. Post-transplant obliterative bronchiolitis and other late lung sequelae in human heart-lung transplantation. Chest 1984; 86(6): 824-829.
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9. Martinu T, Howell DN, Davis RD, Steele MP, Palmer SM. Pathologic correlates of bronchiolitis obliterans syndrome in pulmonary retransplant recipients. Chest 2006; 129(4):1016-1023. 10. Kaditis AG, Phadke S, Dickman P, Webber S, Kurland G, Michaels MG. Mortality after pediatric lung transplantation: autopsies vs. clinical impression. Pediatric Pulmonol 2004; 37(5):413-418. 11. Miller MR, Hankinson J, Brusasco V, et al. Standardisation of spirometry. Eur Respir J 2005; 26(2): 319-338. 12. Wang X, Dockery DW, et al. Pulmonary Function Between 6 and 18 Years of Age. Ped Pulm 1993; 15: 75-88. 13. Stewart S, Fishbein MC, Snell GI, et al. Revision of the 1996 working formulation for the standardization of nomenclature in the diagnosis of lung rejection. J Heart Lung Transplant 2007; 26(12):1229-1242. 14. Martinu T, Howell DN, Davis RD, Steele MP, Palmer SM. Pathologic correlates of bronchiolitis obliterans syndrome in pulmonary retransplant recipients. Chest 2006; 129(4):1016-1023. 15. Sato M, Waddell TK, Wagnetz U, et al. Restrictive allograft syndrome (RAS): A novel form of chronic lung allograft dysfunction. J Heart Lung Transplant 2011; 30: 735742. 16. Burton CM, Iversen M, Mortensen J, et al. Post-transplant baseline FEV1 and the development of bronchiolitis obliterans syndrome: an important confounder? J Heart Lung Transplant 2007; 26(11): 1127-1134. 17. Choong CK, Haddad FJ, Huddleston CB, et al. Role of open lung biopsy in lung transplant recipients in a single children’s hospital: A 13-year experience. J Thorac Cardiovasc Surg 2006; 131: 204-208.
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Figure Legends Figure 1 – After the 370 pediatric lung transplants, 139 open lung biopsies (OLB) and 43 lung explants were performed. 72 OLB and 12 explants were excluded for the reasons listed leaving 67 OLB and 31 explants which underwent further analysis.
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Table Legends Table 1 – Patient characteristics at the time of pathologic diagnosis for the group overall, those with open lung biopsies and those with explants. Results reported as either percent or mean ± standard deviation.
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Table 2 – Patient characteristics at the time of pathologic diagnosis for those with and without bronchiolitis obliterans syndrome. Results reported as mean ± standard deviation.
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Table 3 - Sensitivity, Specificity, Positive Predictive Values, Negative Predictive Values, Positive Likelihood Ratios and Negative Likelihood Ratios of bronchiolitis obliterans syndrome for the diagnosis of bronchiolitis obliterans for the group overall, for those patients with 1 year conditional survival post-transplant and for those patients who underwent open lung biopsy. Results reported as calculated value (95% confidence interval).
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Table 4 – List of pathologic diagnoses on open lung biopsy or explant other than bronchiolitis obliterans. Number in parenthesis is incidence if greater than 1.
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