Published online before print June 26, 2006, 10.1148/radiol.2401050562
(Radiology 2006;240:565-573.)
© RSNA, 2006
Relapsing Polychondritis: Prevalence of Expiratory CT Airway Abnormalities1
Karen S. Lee, MD,
Armin Ernst, MD,
David E. Trentham, MD,
William Lunn, MD,
David J. Feller-Kopman, MD and
Phillip M. Boiselle, MD
1 From the Department of Radiology, Center for Airway Imaging (K.S.L., P.M.B.), Division of Pulmonary Medicine (A.E., W.L., D.J.F.), and Division of Rheumatology (D.E.T.), Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Ave, Boston, MA 02215. From the 2004 RSNA Annual Meeting. Received April 4, 2005; revision requested June 2; revision received July 17; accepted August 11; final version accepted September 22.
Address correspondence to P.M.B. (e-mail: pboisell{at}caregroup.harvard.edu).
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ABSTRACT
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Purpose: To retrospectively determine the prevalence of expiratory computed tomographic (CT) abnormalities, including malacia and air trapping, in patients with relapsing polychondritis and to retrospectively determine the frequency with which expiratory abnormalities are accompanied by inspiratory abnormalities on CT scans.
Materials and Methods: Institutional review board approval was obtained, and informed consent was not required for this retrospective HIPAA-compliant study. A computerized hospital information system was used to identify all patients with clinically diagnosed or biopsy-proved relapsing polychondritis who were referred for CT airway imaging during a 17-month period. The study cohort comprised 18 patients (15 women, three men; mean age, 47 years; age range, 20–71 years). Multidetector helical CT was performed in all patients by using a standard protocol, which included end-inspiratory and dynamic expiratory volumetric imaging. Two observers who were blinded to the original scan interpretations simultaneously reviewed CT scans. Findings were recorded in consensus. Dynamic expiratory CT scans were assessed for malacia that involved the trachea and main bronchi (reduction in cross-sectional area of more than 50%) and for air trapping (failure of lung parenchyma to increase in attenuation during expiration). Air trapping was visually classified according to pattern and extent (lobular, segmental, lobar, or whole lung). Inspiratory CT scans were evaluated for tracheal and bronchial stenosis (>25% luminal diameter narrowing compared with a corresponding uninvolved segment), wall thickening (>2 mm), and calcification.
Results: Expiratory CT abnormalities were present in 17 (94%) of 18 patients and included malacia in 13 patients (72%) and air trapping in 17 patients (94%). Inspiratory CT abnormalities were found in eight (47%) of 17 patients who had expiratory CT abnormalities. Calcification of the airway walls was present in seven (39%) of 18 patients. All patients who had inspiratory CT abnormalities demonstrated expiratory CT abnormalities.
Conclusion: Expiratory CT abnormalities were present in the majority of patients with relapsing polychondritis who were referred for airway imaging, yet only half of these patients demonstrated abnormalities on routine inspiratory CT scans. Thus, dynamic expiratory CT should be a standard component of imaging assessment in patients with relapsing polychondritis.
© RSNA, 2006
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INTRODUCTION
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Relapsing polychondritis is a rare multisystemic disease that is characterized by recurrent inflammation of the cartilaginous structures of the external ear, nose, peripheral joints, larynx, and tracheobronchial tree (1). Relapsing polychondritis is considered very rare, with an estimated annual incidence of 3.5 cases per million in Rochester, New York, and more than 600 cases reported worldwide (2). Airway involvement is present in up to 50% of patients with relapsing polychondritis and is a major cause of morbidity and mortality (1,3,4). Indeed, mortality due to respiratory involvement reportedly accounts for up to 50% of the deaths from this disorder (1,3,4).
Multidetector computed tomography (CT) can visibly demonstrate the classic morphologic airway changes associated with relapsing polychondritis, including fixed airway narrowing and wall thickening with or without calcification. At CT, the finding of smooth anterior and lateral airway wall thickening with sparing of the posterior membranous wall is virtually pathognomonic of relapsing polychondritis (5–10). These changes are thought to occur secondary to cartilaginous destruction and fibrotic replacement and thus reflect relatively late airway manifestations of relapsing polychondritis (5,11).
In patients with relapsing polychondritis, functional airway abnormalities, including malacia and air trapping, likely occur secondary to mucosal edema and cartilaginous inflammation (5,11,12). These changes, which can be detected with dynamic expiratory CT, may be the only airway abnormalities identified during the early stages of relapsing polychondritis (8–11,13).
Importantly, patients with relapsing polychondritis who have airway malacia often have a poorer prognosis than those who do not have this complication. Such patients may be more symptomatic than those without malacia (eg, these patients may experience more frequent recurrent pneumonias) and often require tracheobronchial stent placement (11,14,15). Because early aggressive treatment may potentially delay or prevent irreversible cartilaginous destruction, identification of airway involvement in the initial stages of relapsing polychondritis is important (12).
Despite the potential importance of functional airway disease in patients with relapsing polychondritis, only limited data exist in the literature regarding its prevalence. Behar et al (8) reported the results of expiratory CT in six patients with relapsing polychondritis, three of whom demonstrated malacia and air trapping. On the basis of these data, the authors recommended that expiratory CT should become a part of the routine CT evaluation for patients with relapsing polychondritis. To date, however, the routine use of expiratory CT for evaluation of airway involvement in a consecutive series of patients with relapsing polychondritis has not been assessed to our knowledge.
Thus, the purpose of our study was to retrospectively determine the prevalence of expiratory CT abnormalities, including malacia and air trapping, in patients with relapsing polychondritis patients and to retrospectively determine the frequency with which expiratory abnormalities are accompanied by inspiratory abnormalities on CT scans.
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MATERIALS AND METHODS
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Patients
The institutional review board at our hospital approved the review of radiologic and clinical data for this study. Informed consent was not required for retrospective analysis. Patient confidentiality was protected. Our study was compliant with the requirements of the Health Insurance Portability and Accountability Act.
Our computerized hospital information system was used to identify all patients with clinically diagnosed or biopsy-proved relapsing polychondritis who were referred for CT airway imaging because of respiratory signs or symptoms during a 17-month period (December 2002 though April 2004). Nineteen consecutive patients were initially identified. One patient, however, was excluded from the study because of an inability to cooperate with expiratory breathing instructions. Thus, the final study cohort comprised 18 patients (15 women, three men; mean age, 47 years; age range, 20–71 years). One author (K.S.L.) reviewed each patient's computerized hospital information system records to identify a history of tobacco use, asthma, or chronic obstructive pulmonary disease—all of which are factors that may independently result in air trapping and/or malacia (16–19). Additionally, for patients who underwent bronchoscopy within 2 months of CT, bronchoscopic reports were reviewed and compared with CT findings by two authors (K.S.L., P.M.B.), and agreement was reached by consensus.
Imaging Technique
All patients underwent imaging with an eight–detector row helical CT scanner (LightSpeed; GE Medical Systems, Milwaukee, Wis) with a gantry rotation time of 0.5 second. Patients were imaged with our department's standard CT central airway protocol, which includes imaging performed during two different phases of respiration—that is, end-inspiratory imaging (performed during suspended end inspiration) and continuous dynamic expiratory imaging (performed during forceful exhalation). Prior to helical CT scanning, initial scout topographic images were obtained to determine the area of coverage, which included the trachea and central bronchi. This area corresponded to a length of approximately 10–12 cm.
Helical CT scanning was performed in the craniocaudal direction for both end-inspiratory and dynamic expiratory imaging. End-inspiratory scanning (170 mAs, 120 kVp, 2.5-mm collimation, and high-speed mode, with pitch equivalent of 1.5) was performed first in all cases. After end-inspiratory imaging, patients were coached with instructions for the dynamic expiratory scanning (40 mAs, 120 kVp, 2.5-mm collimation, and high-speed mode, with pitch equivalent of 1.5). For this sequence, patients were instructed to take a deep breath and to exhale during the CT acquisition, which was coordinated to begin with the onset of the patient's forced expiratory effort. To minimize radiation exposure, a low-dose technique (40 mAs) was employed for the dynamic expiratory sequence. The use of a low-dose technique for expiratory imaging of the central airways has been validated by Zhang et al (20). For all cases, multiplanar reformation and three-dimensional internal and external renderings were obtained to aid the assessment of airway stenoses (21).
Image Analysis
Two observers (P.M.B. and K.S.L., with 15 and 2 years of experience in chest CT, respectively) were blinded to the original CT scan interpretations and reviewed images on a picture archiving and communication system (PathSpeed; GE Medical Systems); findings were recorded in consensus. Standard lung (level, –650 HU; width, 1500 HU) and soft-tissue (level, 50 HU; width, 350 HU) window settings were used for display on the workstation. Inspiratory CT scans were systematically assessed for tracheal and bronchial stenosis, airway wall thickening, and airway wall calcification. Airway stenosis was evaluated by comparing the diameter of a narrowed segment with that of a corresponding uninvolved segment. Stenosis was present if luminal diameter narrowing of more than 25% was identified (8). Airway wall thickening was determined to be present if the thickness of the wall of the involved segment of the trachea or main bronchi was greater than 2 mm (22). The distribution of wall thickening, which was classified as either circumferential or sparing the posterior wall, was also noted. Airway calcification was evaluated by comparing the attenuation of the airway wall with that of the surrounding mediastinal soft tissues on images viewed with the standard soft-tissue window.
Dynamic expiratory scans were examined for airway malacia and air trapping immediately after the inspiratory scans were reviewed. All of the expiratory scans were initially compared with their respective inspiratory scans in order to verify that the expiratory scans were acquired during expiration. The following expiratory criteria were used for this visual assessment: (a) narrowing of the anteroposterior dimension of the thorax, (b) a general increase in the attenuation of the lung parenchyma, and (c) flattening or anterior bowing of the posterior membranous wall of the trachea on the expiratory scan compared with the inspiratory scan (23).
To assess for malacia, the dynamic expiratory scans were first visually inspected for the airway segment that demonstrated maximal collapse. By using the computerized tracing tool that was available as part of our hospital's picture archiving and communication system, one observer (P.M.B.) traced the inner wall of the airway by hand at the level of maximal collapse in order to calculate the cross-sectional area of the airway in square millimeters. The cross-sectional area of the airway lumen at a similar level on the end-inspiration scan was then obtained by using the same tracing method. To calculate the percentage of luminal collapse, the dynamic expiratory cross-sectional area was subtracted from the end-inspiratory cross-sectional area and then divided by the end-inspiratory cross-sectional area and multiplied by 100. Malacia was determined to be present if the percentage of luminal collapse at dynamic expiration was greater than 50% (Fig 1) (23). The distribution of malacia involving the trachea, bronchi, or both was also recorded.
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Figure 1a: Transverse (a) end-inspiratory and (b) dynamic expiratory CT scans demonstrate cross-sectional area of the airway lumen (white outline). Measurements were obtained by using an analysis tool on our picture archiving and communication system software. A reduction in cross-sectional area of more than 50% is seen in b, which indicates the presence of malacia. Tracing lines have been electronically thickened to enhance visibility for photographic reproduction.
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Figure 1b: Transverse (a) end-inspiratory and (b) dynamic expiratory CT scans demonstrate cross-sectional area of the airway lumen (white outline). Measurements were obtained by using an analysis tool on our picture archiving and communication system software. A reduction in cross-sectional area of more than 50% is seen in b, which indicates the presence of malacia. Tracing lines have been electronically thickened to enhance visibility for photographic reproduction.
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Air trapping was defined as present if more than 25% of the cross-sectional area of the lung contained hypoattenuating regions on dynamic expiratory scans (24). The pattern of air trapping was visually classified as lobular, segmental, lobar, or whole lung (24). The lobular pattern was defined as areas of air trapping that corresponded to secondary pulmonary lobules or multiple adjacent lobules but involved less than an entire segment. The segmental pattern was defined as air trapping that involved an entire segment or multiple adjacent segments but not an entire lobe. The lobar pattern was defined as involvement of the entire lobe. The whole-lung pattern was defined as involvement of an entire lung. If more than one type of pattern was present, it was classified as a mixed pattern.
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RESULTS
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Inspiratory CT
During inspiratory CT, morphologic abnormalities were present in eight (44%) of 18 patients with relapsing polychondritis (Tables 1, 2). Airway wall thickening was identified in six (33%) of 18 patients (Fig 2). Tracheal and bronchial wall thickening were present in five (28%) of 18 patients, and tracheal wall thickening alone was present in one (6%). In all six patients with airway wall thickening, the posterior membranous wall was spared. Calcification that involved the airway walls with sparing of the posterior membranous wall was seen in seven (39%) of 18 patients and was accompanied airway wall thickening in five (28%) of 18 patients (Fig 2). Airway stenosis was present in five (28%) of 18 patients (Fig 3). Tracheal and bronchial stenosis was identified in four (22%) of 18 patients, and isolated bronchial stenosis was demonstrated in one (6%).
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Figure 2a: Transverse end-inspiratory CT scans of (a) the trachea at the level of the aortic arch and (b) the main bronchi demonstrate smooth tracheal and bronchial wall thickening with calcification. Sparing of the posterior membranous walls of the airways can be seen, which is a classic feature of relapsing polychondritis. Functional abnormalities were also observed in this patient at dynamic expiratory CT.
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Figure 2b: Transverse end-inspiratory CT scans of (a) the trachea at the level of the aortic arch and (b) the main bronchi demonstrate smooth tracheal and bronchial wall thickening with calcification. Sparing of the posterior membranous walls of the airways can be seen, which is a classic feature of relapsing polychondritis. Functional abnormalities were also observed in this patient at dynamic expiratory CT.
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Figure 3: Three-dimensional external rendering of airways viewed from an anterior perspective in patient with relapsing polychondritis demonstrates narrowing of intrathoracic trachea (black arrows) and left main bronchus (white arrows), thereby indicating the presence of diffuse tracheobronchial stenosis.
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Expiratory CT
All dynamic expiratory CT scans were determined to have met the visual criteria for confirmation of the expiratory phase of respiration. On dynamic expiratory CT scans, functional abnormalities were identified in 17 (94%) of 18 patients (Tables 1, 2). Airway malacia was seen 13 (72%) of 18 patients (Figs 4, 5). Tracheobronchomalacia was present in nine (50%) of 18 patients, isolated bronchomalacia in three (17%), and isolated tracheomalacia in one (6%).
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Figure 4a: Severe tracheomalacia and lobular air trapping in patient with relapsing polychondritis. (a) Transverse end-inspiratory CT scan demonstrates trachea with widened coronal diameter and relatively narrow anteroposterior diameter. (b) Transverse dynamic expiratory CT scan at a similar level shows near complete collapse of the trachea, which is consistent with severe tracheomalacia. Lobular air trapping (arrows) is present in both upper lobes.
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Figure 4b: Severe tracheomalacia and lobular air trapping in patient with relapsing polychondritis. (a) Transverse end-inspiratory CT scan demonstrates trachea with widened coronal diameter and relatively narrow anteroposterior diameter. (b) Transverse dynamic expiratory CT scan at a similar level shows near complete collapse of the trachea, which is consistent with severe tracheomalacia. Lobular air trapping (arrows) is present in both upper lobes.
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Figure 5a: Tracheomalacia and mixed air trapping pattern in patient with relapsing polychondritis. (a) Transverse end-inspiratory CT scan of trachea shows normal results. (b) Transverse dynamic expiratory CT scan at a similar level demonstrates excessive collapse of the trachea, which is consistent with tracheomalacia. Bilateral lobular air trapping (black outlined area) is seen in the upper lobes and segmental air trapping (white outlined area) is seen in the superior segment of the left lower lobe.
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Figure 5b: Tracheomalacia and mixed air trapping pattern in patient with relapsing polychondritis. (a) Transverse end-inspiratory CT scan of trachea shows normal results. (b) Transverse dynamic expiratory CT scan at a similar level demonstrates excessive collapse of the trachea, which is consistent with tracheomalacia. Bilateral lobular air trapping (black outlined area) is seen in the upper lobes and segmental air trapping (white outlined area) is seen in the superior segment of the left lower lobe.
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Air trapping was observed in 17 (94%) of 18 patients (Figs 4, 5). The most common pattern of air trapping was lobular, which was seen in nine patients (50%). The remaining cases of air trapping were characterized as segmental in four (22%) of 18 patients, as lobar in one (6%), and as whole lung in one (6%). A mixed pattern of lobular and segmental air trapping was visualized in two patients (11%).
Of the 17 patients who exhibited functional abnormalities (malacia and/or air trapping) on dynamic expiratory CT scans, nine (53%) had normal inspiratory CT findings that did not demonstrate any morphologic abnormalities (Fig 6). Two (22%) of the nine patients who demonstrated isolated functional airway abnormalities without morphologic airway changes had other underlying conditions that could potentially be confounding factors. One patient who demonstrated both malacia and air trapping had a history of asthma, which may also be associated with air trapping (16,17). Another patient who demonstrated malacia and air trapping had chronic obstructive pulmonary disease, which may have contributed to the functional airway abnormalities (18,19).
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Figure 6: Bar graph demonstrates the prevalence of inspiratory and expiratory CT abnormalities in patients with relapsing polychondritis who had morphologic abnormalities at end-inspiratory CT (left column), functional abnormalities at dynamic expiratory CT (middle column), or imaging abnormalities at expiratory CT only (right column).
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All eight patients with inspiratory CT abnormalities had evidence of expiratory CT abnormalities.
Bronchoscopy
Bronchoscopy of the trachea and bronchi was attempted in six patients. In one patient, however, the central airways could not be assessed with bronchoscopy. Thus, comparative results for bronchoscopy of the trachea and bronchi were available for five patients in our series (Table 1). There was agreement between bronchoscopic and CT findings in the two cases of airway stenosis (one case of tracheal and bronchial stenosis and one case of bronchial stenosis). Bronchoscopic findings confirmed the presence of malacia in all five patients who had CT evidence of malacia and who underwent bronchoscopy. In one case, however, there was a discrepancy in the extent of malacia, which was classified as tracheobronchomalacia at CT and as isolated bronchomalacia at bronchoscopy.
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DISCUSSION
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The results of our study show that expiratory CT abnormalities are present in most patients with relapsing polychondritis who possess pulmonary symptoms and that about half of these patients have normal results at inspiratory CT. These findings indicate that dynamic expiratory CT is an important method for identifying airway involvement in patients with relapsing polychondritis. Thus, we believe that dynamic expiratory CT should be considered as a routine component of imaging for patients with relapsing polychondritis in whom there is clinical suspicion for airway involvement.
Our findings are concordant with the proposed natural history of airway disease in patients with relapsing polychondritis, during which functional airway abnormalities such as malacia and air trapping are thought to occur secondary to mucosal edema and cartilaginous inflammation (5,11,12). These changes, which can be detected with dynamic expiratory CT, may be the only airway abnormalities identified during the early stages of relapsing polychondritis (8–11,13). Because early aggressive treatment may potentially delay or prevent irreversible cartilaginous destruction, identification of airway involvement in the initial stages of relapsing polychondritis is important (12). Because respiratory involvement reportedly accounts for up to 50% of the deaths from relapsing polychondritis (1,3,4), the early diagnosis and treatment of central airway disease could have a major effect on mortality.
Although both airway malacia and air trapping have been described in a small number of patients with relapsing polychondritis (8,13), to our knowledge, we are the first to have systematically performed expiratory CT in a consecutive series of patients with relapsing polychondritis who were referred for CT evaluation of the airways. Behar et al (8) previously reported CT findings in 15 patients with relapsing polychondritis who underwent CT scanning. In their series, six patients underwent expiratory imaging, three of whom showed evidence of air trapping and malacia. The authors suggested that expiratory CT should be routinely applied to the evaluation of patients with relapsing polychondritis. Our results provide the necessary evidence from a larger cohort of patients to support this recommendation.
In comparison with the results of Behar et al (8), the results of our cohort demonstrate a higher prevalence of expiratory CT abnormalities. The reason for the lower prevalence of airway malacia and air trapping in the series by Behar et al compared with that in our study (50% vs 94%, respectively) may be related to differences in the type of expiratory imaging that was employed, as well as to differences in the types of methods used. Behar et al employed end-expiratory imaging (imaging at the end of exhalation), whereas we employed dynamic expiratory imaging (imaging during forced exhalation). The results of previous investigations have shown that dynamic expiratory imaging elicits a greater degree of air trapping and malacia than does end-expiratory imaging (25,26). For example, Baroni et al (26) demonstrated that, compared with dynamic expiratory imaging, end-expiratory imaging can result in an unacceptably high rate of false-negative findings for malacia. Thus, our method of dynamic expiratory CT was likely more sensitive in demonstrating malacia and air trapping than was the technique employed by Behar et al.
With regard to air trapping, it should also be noted that our methods differed from those used by Behar et al in that we considered any pattern of air trapping to be abnormal if more than 25% of the lung was involved (24). In contrast, Behar et al did not record cases in which air trapping involved less than an entire segment; this likely resulted in an underestimation of the prevalence of air trapping in their series. Finally, the smaller number of patients (n = 6) that underwent expiratory imaging in the study by Behar et al may not have been reflective of the entire group of patients in their series.
In our study, we detected malacia in nearly 75% of patients with relapsing polychondritis, many of whom had normal findings at inspiratory CT. If expiratory CT had not been performed, many of these patients would have had a "normal" CT report, with no findings to account for their symptoms. The identification of malacia is important in this population because researchers have reported that patients with relapsing polychondritis and malacia may have a poorer prognosis than those with relapsing polychondritis and no malacia (11,14,15). Such patients may be more symptomatic than those without malacia (eg, these patients may experience more frequent recurrent pneumonias) and often require tracheobronchial stent placement (11,14,15). Thus, although dynamic expiratory CT is clearly indicated in patients with relapsing polychondritis who have normal results at inspiratory CT, we believe that the use of dynamic expiratory CT is also justified in those who have abnormal results at inspiratory CT because the identification of malacia has potential prognostic and therapeutic indications.
Interestingly, many of the patients with malacia in our study also demonstrated air trapping. An association between air trapping and malacia has been previously reported by our group, which demonstrated that air trapping occurs with higher frequency and greater severity among patients who have malacia than among those who do not have this condition (24). We previously postulated that air trapping in patients with airway malacia occurs because of chronic small-airway disease that results from difficulty clearing airway secretions and recurrent infections. The mechanism of air trapping in individuals with relapsing polychondritis and malacia is thus hypothesized to result from cartilaginous inflammation that causes weakening of the airway walls, thereby leading to impaired airway dynamics and poor clearance of secretions, which results in small-airway disease.
Regarding the four patients in our series with isolated air trapping and no evidence of malacia or other airway abnormalities, it is uncertain whether this finding is due to the distal airway involvement of relapsing polychondritis, which has previously been considered a rare manifestation of this disease (27), or whether other factors may have contributed to this finding. Longitudinal follow-up of this subset of patients would help determine whether central airway abnormalities develop over time.
There are several limitations of our study. First, longitudinal imaging data are not yet available for this cohort.
Second, although there was agreement between CT and bronchoscopic results in the patients who underwent both of these tests, fewer than half of the patients in this cohort underwent bronchoscopy. We emphasize that bronchoscopy is not routinely performed in this population because the procedure has been reported to exacerbate airway inflammation (1).
Third, because pulmonary function tests were not routinely obtained in our cohort, we were not able to compare CT results with pulmonary function studies.
Fourth, our study lacks information regarding the time interval between symptom onset and CT scanning. Because patients with relapsing polychondritis often present with ambiguous findings and nonspecific symptoms, there is often a substantial delay between the time medical attention is sought for symptom onset and the time of eventual diagnosis. Therefore, as a result of the ambiguous nature of symptoms and the difficulty in diagnosis, the exact time interval between symptom onset and CT scanning cannot be determined fully for this cohort. A future prospective study would be helpful in this regard. Future studies comparing functional airway abnormalities with pulmonary function tests would be valuable and may support the presence of small-airway disease as a cause of the air trapping.
Finally, our study had a selection bias because only patients with respiratory signs or symptoms were referred for airway imaging. Imaging a cohort of patients with relapsing polychondritis who are asymptomatic would be of use to determine whether functional airway changes can precede the development of symptoms.
In conclusion, the results of our study demonstrate that expiratory CT abnormalities are a very common finding in patients with relapsing polychondritis who are symptomatic and that many of these patients have normal inspiratory CT findings. Therefore, we believe that dynamic expiratory CT should be considered a standard component of airway evaluation in patients with relapsing polychondritis.
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ADVANCES IN KNOWLEDGE
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- Expiratory CT airway abnormalities (ie, malacia and air trapping) were seen in the majority of patients with relapsing polychondritis who were referred for airway imaging, many of whom demonstrated normal findings at inspiratory CT.
- Dynamic expiratory CT should be a standard component of airway imaging assessment in patients with relapsing polychondritis.
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FOOTNOTES
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Authors stated no financial relationship to disclose.
Author contributions: Guarantors of integrity of entire study, K.S.L., P.M.B.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, all authors; clinical studies, K.S.L., P.M.B.; and manuscript editing, all authors
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INTRODUCTION
