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Keywords:

  • fibroblastic focus;
  • non-specific interstitial pneumonia;
  • pulmonary function;
  • usual interstitial pneumonia

ABSTRACT

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgement
  8. REFERENCES

Background and objective:  Fibroblastic foci (FF) composed of an accumulation of fibroblasts or myofibroblasts may be related to the progression of pulmonary fibrosis leading to respiratory insufficiency. Several studies have shown that the number of FF is a significant prognostic factor in usual interstitial pneumonia (UIP). The purpose of the present study was to examine whether the extent of FF is related to impairment of respiratory function and prognosis in patients with biopsy-proven fibrosing interstitial pneumonia, including UIP and fibrotic non-specific interstitial pneumonia (fNSIP).

Methods:  Fifty patients with histologically confirmed interstitial pneumonia including UIP or fNSIP were investigated, and correlations between FF and pulmonary function were evaluated. FF area was calculated as the proportion of total area (%FF) and the number of FF (FF/cm2) in the whole histological specimen from each patient.

Results:  The UIP group showed significantly higher %FF and FF/cm2 than the fNSIP group. When UIP and fNSIP patients were analysed together, the group of patients who had died (death group) revealed significantly higher %FF and FF/cm2 compared with the group of survivors, and the impairment of vital capacity and diffusing capacity of carbon monoxide was correlated with %FF and FF/cm2.

Conclusions:  FF correlated with impaired pulmonary function and may be a useful parameter to predict prognosis in patients with UIP and fNSIP.


Abbreviations:
DLCO

diffusing capacity of carbon monoxide

FF

fibroblastic foci

fNSIP

fibrotic non-specific interstitial pneumonia

UIP

usual interstitial pneumonia

VC

vital capacity

INTRODUCTION

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgement
  8. REFERENCES

Fibroblastic foci (FF) are characteristic features of usual interstitial pneumonia (UIP) and are associated with progression of disease and a poor prognosis.1–3 They are composed of aggregates of mesenchymal cells including fibroblasts and myofibroblasts and may play a critical role in the progression of pulmonary fibrosis.

There has been an interest in the prognostic significance of FF in UIP. Several studies have demonstrated the clinical importance of FF as a prognostic parameter, establishing that poor prognosis is related to a greater number of FF.1–3 However, some studies have failed to demonstrate the correlation between FF and survival in patients with idiopathic pulmonary fibrosis, indicating that quantitative assessment of FF in surgical lung biopsy specimens is of limited prognostic value.4–6 These conflicting results are probably a result of the different methods used to select samples from patients. In the previous studies, FF was examined only in UIP, not in non-specific interstitial pneumonia. Furthermore, previous studies analysed FF in selected areas of lung specimens using a score grading system, not in the whole specimen.7 In addition, a recent guideline indicates that surgical lung biopsy is not essential in the subjects showing UIP pattern on high-resolution computed tomography. As a result, biopsy would be performed only in patients with the difficulty in computed tomography diagnosis. This could cause a difficulty to distinguish histologically between UIP and fibrotic non-specific interstitial pneumonia (fNSIP). The purpose of the present study was to examine whether the extent of FF is related to impairment of respiratory function and prognosis in patients with biopsy-proven fibrosing interstitial pneumonia, including UIP and fNSIP.

METHODS

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgement
  8. REFERENCES

Patients

We reviewed patients with interstitial pneumonia who had open or a video-assisted thoracoscopic lung biopsy in Fukuoka University Hospital, National Hospital Organization Kyushu Medical Center, and Fukuoka National Hospital between 1995 and 2008. Fifty patients with histologically confirmed UIP or fNSIP were selected. Patients with concomitant lung neoplasms were excluded. Histological diagnosis of UIP and fNSIP was based on a previously published report8 and the criteria in the American Thoracic Society/European Respiratory Society consensus classification.9 The study protocol was approved by the ethics committee of our institute.

Pathological evaluation

The specimens were routinely fixed in 10% formalin and were processed into paraffin blocks for histopathological examination. Tissue sections were cut 4 µm thick and stained with HE, Alcian blue-periodic acid Schiff and elastica van Gieson.

FF, newly formed connective tissue bundles, were defined as subepithelial, interstitial areas in which fibroblasts and myofibroblasts were arranged in a linear manner within a pale staining matrix and which were stained blue by Alcian blue-periodic acid Schiff (Fig. 1).

image

Figure 1. A histopathological example of fibroblastic foci. (a) HE section. Fibroblastic foci are composed of aggregates of fibroblasts or myofibroblasts arranged in a linear manner within a pale staining matrix. Scale bars = 200µm. Original magnification × 200. (b) Alcian blue-periodic acid Schiff (AB-PAS) section. Matrix of fibroblastic foci is stained blue. Scale bars = 200µm. Original magnification × 200.

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The area of FF and the whole lung tissue area were measured using image analysis software (WinROOF version 5.5, Mitani Corporation, Fukui, Japan). The total number of FF was obtained by counting all FF in all specimens from each patient, and FF/cm2 was calculated by dividing the total number of FF by the whole lung tissue area (cm2). %FF was calculated by dividing the total area of FF by the whole lung tissue area.

Respiratory function data

All respiratory function data, including vital capacity (VC) and diffusing capacity (diffusing capacity of carbon monoxide (DLCO)) during the entire follow-up period, were obtained from the medical records. Annual changes in respiratory function were estimated from linear regressions, assuming time dependency and linearity. Percentage decrease from the baseline per year (%ΔVC, %ΔDLCO) was obtained from the linear equation, and the correlation between the respiratory function impairment and FF was evaluated.

Statistical analysis

Numerical data are presented as the mean ± standard error of the mean. For analysis, the unpaired Student's t-test was used for pairwise comparisons. Categorical data were compared between UIP and fNSIP using the chi-square test for independence. Prognostic data were analysed using the Kaplan–Meier curve with log–rank test. Correlations involving FF and respiratory function data were evaluated using the Spearman rank coefficient. Statistical analysis was performed with StatView software for Windows version 5.0 (SAS Institute Inc., Cary, NC, USA). P-values less than 0.05 were considered significant.

RESULTS

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgement
  8. REFERENCES

Clinical characteristics, laboratory and physiological findings

The patient population consisted of 28 males and 22 females; mean age was 61.2 years. Of the 50 patients, 24 (48.0%) were diagnosed with UIP and 26 (51.0%) with fNSIP. The clinical characteristics and laboratory findings of the patients are summarized in Table 1.

Table 1. Clinical characteristics, and laboratory and physiological findings of the study population
VariablesUIPNSIP P-value
  • P < 0.05.

  • DLCO, diffusing capacity of carbon monoxide; KL-6, Krebs von den Lungen-6; LDH, lactate dehydrogenase; NSIP, non-specific interstitial pneumonia; PaO2, partial pressure of oxygen (arterial); UIP, usual interstitial pneumonia; VC, vital capacity.

Clinical characteristics   
 Male/female gender, No.15/913/130.3737
 Age at biopsy, year65.3 ± 9.857.4 ± 11.50.0120*
 Pack years of smoking18.4 ± 28.919.0 ± 30.00.9476
 Month since onset of symptoms24.3 ± 37.812.3 ± 16.00.2064
Laboratory findings   
 Serum KL-6, U/mL1075 ± 6152190 ± 22630.0423*
 Serum LDH, IU298 ± 191286 ± 1210.7930
Physiological findings   
 VC, %predicted72.5 ± 18.885.5 ± 16.20.0387*
 DLCO, %predicted70.6 ± 23.482.9 ± 20.30.1261
 PaO2 at room air, torr81.5 ± 14.183.5 ± 11.10.6181

Of the clinical characteristics, age at lung biopsy was significantly different between UIP and fNSIP. Of 50 cases, 9 were current smokers, 13 were ex-smokers and 28 were never smokers. Serum Krebs von den Lungen-6 levels differed significantly between UIP and fNSIP groups (UIP < fNSIP).

Collagen vascular disease was found in five cases from the UIP group and four cases from the fNSIP group during the follow-up period.

Quantitative analysis of FF: Comparison between UIP and fNSIP, and between death and survival groups

Of 50 cases in our study, 9 cases had one biopsy sample and 41 patients had multiple biopsy samples. We divided all the samples into four groups based on biopsied sites (i.e. upper lobe, middle lobe, lingula and lower lobe). Nineteen per cent were obtained from upper lobe, 21% from middle lobe, 12% from lingula and 48% from lower lobe.

In UIP patients, %FF (0.266 ± 0.233) and FF/cm2 (7.07 ± 45.12) were significantly higher than in fNSIP patients: %FF (0.045 ± 0.054) (P < 0.0001, Fig. 2a) and FF/cm2 (1.69 ± 2.07) (P < 0.0001, Fig. 2b).

image

Figure 2. Quantitative analysis of fibroblastic foci in the whole specimen. (a) The areal percentage of fibroblastic foci was significantly higher in usual interstitial pneumonia (UIP) group than in non-specific interstitial pneumonia (NSIP) group. (b) The number of fibroblastic foci was significantly higher in UIP group than in NSIP group. Data are mean ± standard deviation.

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We investigated the area of normal lung, fibrosis and honeycomb lung by reviewing the available samples of 30 patients. In fNSIP, the area of normal lung to fibrosis was 40.7 ± 29.4% and 59.3 ± 29.4%, respectively, and in UIP, 36.5 ± 34.3% and 63.5 ± 34.3%, respectively (not significant). Among fibrosis, the honeycombing area was 4.8 ± 10.3% in fNSIP and 24.6 ± 24.7% in UIP, a significant difference (P = 0.0284).

Since follow up was done in all patients, we divided these into those who died (death group, n = 13) and those who survived (survival group, n = 37) and compared %FF and FF/cm2 between the groups. The mean follow-up period for the survival group and the mean survival period for the death group were 55.2 months and 33.6 months, respectively. %FF in the death group (0.292 ± 0.259) was significantly higher than in the survival group (0.101 ± 0.106) (P = 0.0020, Fig. 3a). FF/cm2 in the death group (7.45 ± 6.17) was also higher than in the survival group (3.16 ± 3.49) (P = 0.0034, Fig. 3b). Significant differences in %FF and FF/cm2 between the two groups were also demonstrated when only UIP patients were analysed, but results for fNSIP patients only showed no significance (data not shown).

image

Figure 3. Quantitative analysis of fibroblastic foci of all cases comparing death group and survival group. (a) The areal percentage of fibroblastic foci was significantly higher in death group than in survival group. (b) The number of fibroblastic foci was significantly higher in death group than in survival group. Data are mean ± standard deviation.

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We reviewed the prognosis and clinical course for all patients enrolled in this study to draw the Kaplan–Meier curve. Significant prognostic difference between UIP and fNSIP was demonstrated by log–rank test (P = 0.0233, Fig. 4).

image

Figure 4. Kaplan–Meier curve of patients enrolled in the study. Patients with fibrotic non-specific interstitial pneumonia (fNSIP) survived significantly longer than those with usual interstitial pneumonia (UIP) by log–rank test (P = 0.0233).

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Correlation between FF and respiratory function parameters

The initial value of %VC has an inverse correlation with FF/cm2 when UIP and fNSIP patients were analysed together (rs = 0.211, Fig. 5a). Also, as shown in Figure 5b,c, %ΔVC was correlated with both %FF and FF/cm2 (rs = 0.333 and 0.294). %ΔDLCO was correlated only with %FF (rs = 0.268, Fig. 5d). However, the initial value of %DLCO did not have any obvious correlation with FF. When the UIP and fNSIP patients were analysed separately, no significant correlations were observed (data not shown).

image

Figure 5. Correlation between pulmonary function and fibroblastic foci (FF). %FF and the number of FF correlated inversely with (a) % vital capacity (VC) and (b,c) %ΔVC (a: rs = 0.211; b: rs = 0.333; c: rs = 0.294); (d) %Δ diffusing capacity of carbon monoxide correlated only with %FF (rs = 0.268). (●) fNSIP, fibrotic non-specific interstitial pneumonia; (○) UIP, usual interstitial pneumonia.

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DISCUSSION

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgement
  8. REFERENCES

This is the first study to examine the area and the number of FF in both UIP and fNSIP samples obtained from surgical lung biopsy. Based on the assumption that FF is a common histological finding in both UIP and fNSIP that reflects disease progression, we examined the relationship between the extent of FF and the respiratory function in a combined group of patients with UIP or fNSIP. A correlation between FF and both respiratory function and prognosis was demonstrated. Our result revealed that the decline in VC and DLCO was significantly correlated with the increasing area and/or number of FF. Furthermore, the group of patients who died had a higher degree of FF compared with the survival group.

There have been various attempts to relate disease progression to the extent of FF.1–7 Most of these studies were performed using UIP samples. However, fNSIP accepts some temporal range in lung injury, allowing the presence of some FF coexistent with old fibrosis (e.g. honeycombing).9–11 These ambiguous criteria might be confusing when making a differentiation between UIP and fNSIP. Furthermore, to what extent FF are considered to exist in the case of an fNSIP pattern remains unclear.

Practically, lung biopsy tends to be performed in patients whose computed tomography patterns are non-UIP-like, and patients with computed tomography patterns typical of UIP rarely have the opportunity to receive a lung biopsy. This may cause difficulty in histologically categorizing interstitial pneumonia. Furthermore, in our fNSIP patients, the time between onset of symptoms and the visit to the hospital was longer than previously reported.12 It is therefore possible that some cases classified as fNSIP in our study could be diagnosed as idiopathic pulmonary fibrosis after consensus clinical, radiological and pathological review. According to the report of an American Thoracic Society project,13 a high-resolution computed tomography showing a pattern typical of UIP, such as honeycombing in the subpleural areas of the bilateral lower lobes, could lead to a diagnosis of idiopathic pulmonary fibrosis even when a surgical lung biopsy shows the histological pattern of fNSIP.

Latsi and co-workers14 analysed the prognosis of idiopathic fibrosing interstitial pneumonia, demonstrating that the distinction between UIP and fNSIP provides no additional prognostic information once serial pulmonary function trends have been taken into account at 12-month follow up. Furthermore, when the initial DLCO was less than 35% predicted, there was no significant difference in outcome between UIP and fNSIP, suggesting that the pathological pattern is less important for prognosis in the setting of relatively severe impairment of lung function. Similarly, patients who exhibit more than 10% decrease in forced VC have a poor outcome, whether they are classified as UIP or fNSIP.15 These data show the role of respiratory function in addition to histological classification as a prognostic indicator. Our results indicate the significance of FF related to deteriorating pulmonary function in fibrosing interstitial pneumonia consisting of UIP and fNSIP.

It is also known that FF represent a measure of UIP activity, being associated with a poor prognosis, and several studies demonstrate the clinical importance of FF as a prognostic factor.1–3 Nicholson and co-workers3 demonstrated that an increasing semiquantitative FF score was independently associated with greater declines in forced VC and DLCO at both 6 months and 12 months. King and co-workers2 demonstrated an association between increasing FF, including the results of semiquantitative grading of the number of FF, and decreased survival in UIP. These data suggest that quantifying the number of these lesions in a biopsy specimen provides additional prognostic information. Moreover, Enomoto and co-workers7 reported quantitative analysis of FF in UIP, showing that the quantitative fibroblast score was a highly significant predictor of outcome in combined analysis of patients with idiopathic pulmonary fibrosis and those with collagen vascular disease. Our results are almost entirely in agreement with these previous investigations. However, the %FF in this study is definitely lower, even in UIP samples, than that reported by Enomoto et al. Their analysis differed from ours in that 10 randomly selected fields were chosen for analysis. These differences in methods for selecting microscopic fields for study may cause the difference in the %FF data.

We have provided evidence of a correlation between FF and pulmonary function in both UIP and fNSIP patients. This result indicates that FF may be another factor predicting the prognosis of fibrosing interstitial pneumonias including both UIP and fNSIP. Increasing degrees of FF and the decline of forced VC or DLCO might be important prognostic predictors for fNSIP as well as for UIP. Given the poor benefit achieved with immunosuppressive or anti-inflammatory agents, these data suggest that future therapies should be aimed at preventing or inhibiting the fibroproliferative response.

Acknowledgement

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgement
  8. REFERENCES

This work was partly supported by a grant to the Diffuse Lung Diseases Research Group from the Ministry of Health, Labour and Welfare, Japan.

REFERENCES

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgement
  8. REFERENCES
  • 1
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    Katzenstein AL, Fiorelli RF. Nonspecific interstitial pneumonia/fibrosis. Histologic features and clinical significance. Am. J. Surg. Pathol. 1994; 18: 13647.
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    Flaherty KR, Martinez FJ, Travis W et al. Nonspecific interstitial pneumonia (NSIP). Semin. Respir. Crit. Care Med. 2001; 22: 42334.
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    Nagai S, Kitaichi M, Itoh H et al. Idiopathic nonspecific interstitial pneumonia/fibrosis: comparison with idiopathic pulmonary fibrosis and BOOP. Eur. Respir. J. 1998; 12: 10109.
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    Travis WD, Hunninghake G, King TE Jr et al. Idiopathic nonspecific interstitial pneumonia. Report of an American Thoracic Society project. Am. J. Respir. Crit. Care. Med. 2008; 177: 133847.
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    Latsi PI, du Bois RM, Nicholson AG et al. Fibrotic idiopathic interstitial pneumonia: the prognostic value of longitudinal functional trends. Am. J. Respir. Crit. Care Med. 2003; 168: 5317.
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    Jegal Y, Kim DS, Shim TS et al. Physiology is a stronger predictor of survival than pathology in fibrotic interstitial pneumonia. Am. J. Respir. Crit. Care Med. 2005; 171: 63944.