Abstract
It is hypothesized that the extent and severity of fibrosis and cellularity found on lung biopsy determine the prognosis and response to therapy in idiopathic pulmonary fibrosis (IPF). The objective of this study was to determine which histopathologic features predict survival in IPF. We prospectively studied 87 patients with usual interstitial pneumonia (UIP) confirmed by surgical lung biopsy. Four pathologists independently graded the extent and severity of specific histopathologic features. We used Cox proportional-hazards models to assess the effect of histopathologic patterns on patients' survival. The effects of age, sex, and smoking were also included in the analysis. Sixty-three patients died during the 17-yr study period. Survival was longer in subjects with lesser degrees of granulation/connective tissue deposition (fibroblastic foci). The degree of alveolar space cellularity, alveolar wall fibrosis, and cellularity did not affect survival. A history of cigarette smoking, the level of dyspnea, and the degree of lung stiffness at presentation were also shown to be independent factors predicting survival. The extent of fibroblastic foci present on lung biopsy predicts survival in IPF. These findings support the hypothesis that the critical pathway to end-stage fibrosis is not “alveolitis” but rather the ongoing epithelial damage and repair process associated with persistent fibroblastic proliferation. Controlling these processes, rather than stopping inflammation, appears most important in preventing progressive disease and the fatal outcome common in IPF.
Keywords: idiopathic pulmonary fibrosis; usual interstitial pneumonia; prospective studies; pulmonary fibrosis physiopathology; smoking physiopathology; survival rate
Idiopathic pulmonary fibrosis (IPF) is a common interstitial lung disease (ILD) of unknown etiology. Clinical deterioration in IPF is expected; 5-yr survival ranges from 30 to 50% (1). Few studies have identified features of IPF that are associated with an increased risk of disease progression and death (2). Reported indicators, at presentation, of longer survival include: younger age (< 50 yr), female, a shorter symptomatic period prior to diagnosis, less dyspnea, preserved lung function, extent of ground-glass and reticular opacities on high-resolution computed tomography (HRCT) scan, lymphocytosis (20 to 25%) in bronchoalveolar lavage fluid (BAL), and a beneficial response or stable disease 3 to 6 mo after initial corticosteroid therapy (2-5). Features associated with shortened survival include: increased neutrophils (> 5%) (6) or eosinophils (> 5%) (2) in the BAL, a failure to respond to immunosuppression therapy, and the extent of “fibrosis” on HRCT scan (5).
The diagnosis of IPF is best confirmed by the identification of usual interstitial pneumonia (UIP) on surgical lung biopsy. The UIP pattern is characterized by heterogeneity that includes patchy chronic inflammation (alveolitis), progressive injury (small aggregates of proliferating myofibroblasts and fibroblasts, termed fibroblastic foci) and fibrosis (dense collagen and honeycomb change) (7).
The correlation between lung pathology and survival is controversial and inadequately defined (7). The most widely held hypothesis suggests that the prognosis and response to therapy of patients with IPF is determined by the extent of cellularity versus fibrosis present on lung tissue examination (8). We carried out a semiquantitative grading of histopathologic abnormalities found on surgical lung biopsy (9-11). The purpose of this article is to report the relative roles of specific histopathologic alterations in determining prognosis in patients with IPF.
The study cohort consisted of 87 patients prospectively enrolled in an ILD Study at the National Jewish Medical and Research Center between 1982 and 1993. The diagnosis of IPF was established according to previously described clinical and histologic criteria (7, 12). Patients with a defined connective tissue disease, left ventricular failure, an occupational and/or environmental exposure that resulted in ILD, or a history of ingestion of a drug or an agent known to cause pulmonary fibrosis were excluded from the study. There were 54 men and 33 women, 89% were white and their ages ranged from 36 to 77 yr (Table 1). Informed consent was obtained from each patient; and the Institutional Human Subject Review Committee approved the protocol. All subjects had clinical, radiographic, and lung function evaluation. Subjects were designated as current smokers (if they smoked cigarettes regularly within the previous year), former smokers (if they had not smoked cigarettes in the previous year but had smoked in the past), and never smokers. Twenty-three were never cigarette smokers, and 64 were ever smokers, including 21 current smokers and 43 former smokers. There were differences in age, sex, and race among the smoking groups.
| Comparisons* | All Patients | Current | Former | Never | ||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| N vs. F | N vs. C | F vs. C | (n) | Median | 25th | 75th | (n) | Median | 25th | 75th | (n) | Median | 25th | 75th | (n) | Median | 25th | 75th | ||||||||||||||||||||
| Age at Biopsy, yr | x | x | 87 | 65.0 | 57.0 | 69.0 | 21 | 53.0 | 47.0 | 64.0 | 43 | 66.0 | 60.0 | 71.0 | 23 | 67.0 | 61.0 | 71.0 | ||||||||||||||||||||
| Sex, Female/Male | x | x | 33/54 (38%) | 6/15 (29%) | 10/33 (23%) | 17/6 (74%) | ||||||||||||||||||||||||||||||||
| Race, White/Nonwhite | x | 77/10 (89%) | 15/6 (71%) | 42/1 (98%) | 20/3 (87%) | |||||||||||||||||||||||||||||||||
| Dyspnea, 0 to 20 scale | 87 | 10.0 | 6.0 | 14.0 | 21 | 10.0 | 8.0 | 14.0 | 43 | 12.0 | 6.0 | 14.0 | 23 | 10.0 | 8.0 | 16.0 | ||||||||||||||||||||||
| Pack-years of smoking | x | x | 87 | 34.0 | 0.0 | 54.0 | 21 | 44.0 | 34.0 | 58.0 | 43 | 46.0 | 22.0 | 63.0 | 23 | 0.0 | 0.0 | 0.0 | ||||||||||||||||||||
| Months since onset of symptoms | 87 | 24.0 | 12.0 | 37.0 | 21 | 30.0 | 12.0 | 48.0 | 43 | 24.0 | 12.0 | 42.0 | 23 | 24.0 | 12.0 | 36.0 | ||||||||||||||||||||||
A modified American Thoracic Society (ATS) questionnaire was used to collect demographic and medical information (13). Information regarding the course of the patient's illness was obtained from the initial history obtained at the time of evaluation and from a follow-up questionnaire. Disease onset was defined as the patient's first recollection of the appearance of cough (coughing throughout the day) or dyspnea (breathlessness walking up inclines) or the first documented chest roentgenogram showing ILD. When a subject had both cough and dyspnea, the onset of the earliest symptom was considered the date respiratory symptoms began. The type and amount of exertion determined the severity of dyspnea required to induce distressful breathing using a previously described dyspnea scale (13).
The methods used for the pulmonary function, volume-pressure relationship, and exercise testing have been described previously (11). Physiologic assessment included measurement of thoracic gas volume (Vtg) and TLC, FVC, and FEV1, the volume-pressure relationship of the lungs, and the single-breath diffusing capacity for carbon monoxide (Dl CO). The coefficient of elastic retraction was calculated by dividing maximal static transpulmonary pressure by TLC. The normal value in our laboratory is 3 to 8 cm H2O/L. The volume-pressure data were also subjected to an exponential curve fit where volume is expressed as a percentage of observed TLC, and the exponential K, a constant that is proportional to the total incremental compliance was derived from the equation: V = A − Be − K p, where V is the volume at a given pressure (p), A is the maximal theoretical volume at infinite pressure, and B is A minus the intercept of the fitted exponential on the volume axis (11).
Respiratory frequency, tidal volume, expired gas concentrations, heart rate, and blood pressure and arterial blood gas tensions were determined at rest and while exercising on an electrically braked bicycle ergometer during incremental work loads (maximal exercise testing), and during steady-state exercise at 50% of the maximum work load achieved during the incremental exercise testing. Arterial blood gases were determined with blood electrodes. The aaPo 2 was calculated from the simplified alveolar air equation. Because approximately half of the patients required supplemental oxygen during exercise, the steady-state exercise PaO2 and aaPo 2 were corrected for Fi O2 , using the equation: Po 2 (corr) = (PaO2 / Fi O2 ) × 21, and aaPo 2 (corr) = aaPo 2/ Fi O2 ) × 21. Dead space to tidal volume ratio (Vd/Vt) was calculated using the Bohr equation and corrected for the additional mechanical dead space imposed by the experimental apparatus: Vd = ((PaCO2 − Pe CO2 )/PaCO2 ) × Vt − minus (mechanical dead space of apparatus). Oxygen consumption (V˙o 2) and maximal work load achieved were expressed as percent of predicted reference values obtained from the age- and sex-adjusted equations of Jones and Campbell (14). As seen in Table 2, there was a considerable range of functional disturbances.
| Comparisons* | All Patients | Current | Former | Never | ||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| N vs. F | N vs. C | F vs. C | (n) | Median | 25th | 75th | (n) | Median | 25th | 75th | (n) | Median | 25th | 75th | (n) | Median | 25th | 75th | ||||||||||||||||||||
| TLC, % pred | x | x | 87 | 81.0 | 68.0 | 92.0 | 21 | 90.0 | 81.0 | 98.0 | 43 | 81.0 | 68.0 | 90.0 | 23 | 74.0 | 67.0 | 79.0 | ||||||||||||||||||||
| Vtg, % pred | 87 | 71.0 | 64.0 | 85.0 | 21 | 84.0 | 65.0 | 95.0 | 43 | 71.0 | 62.0 | 78.0 | 23 | 70.0 | 61.0 | 77.0 | ||||||||||||||||||||||
| FVC, % pred | x | x | 87 | 69.0 | 56.0 | 83.0 | 21 | 79.0 | 72.0 | 86.0 | 43 | 68.0 | 57.0 | 82.0 | 23 | 58.0 | 47.0 | 72.0 | ||||||||||||||||||||
| FEV1, % pred | x | x | 87 | 80.0 | 64.0 | 92.0 | 21 | 82.0 | 73.0 | 89.0 | 43 | 83.0 | 68.0 | 94.0 | 23 | 68.0 | 56.0 | 83.0 | ||||||||||||||||||||
| FEV1/FVC ratio | x | x | 81 | 80.0 | 75.0 | 87.5 | 20 | 76.0 | 68.0 | 80.0 | 39 | 79.0 | 75.0 | 87.0 | 22 | 87.0 | 79.0 | 89.3 | ||||||||||||||||||||
| SGaw, % pred | 82 | 108.5 | 81.0 | 137.0 | 20 | 101.5 | 75.0 | 126.5 | 40 | 122.5 | 89.0 | 148.0 | 22 | 91.0 | 74.0 | 129.0 | ||||||||||||||||||||||
| Coefficient of elastic retraction, cm H20/L | x | x | 79 | 11.0 | 7.4 | 13.9 | 20 | 6.9 | 5.8 | 11.2 | 40 | 11.7 | 8.7 | 13.9 | 19 | 13.4 | 8.3 | 15.8 | ||||||||||||||||||||
| K value, log | 76 | −2.4 | −2.8 | −2.1 | 19 | −2.3 | −2.7 | −1.9 | 39 | −2.4 | −2.8 | −2.1 | 18 | −2.6 | −3.0 | −2.2 | ||||||||||||||||||||||
| Dl CO, % pred | 85 | 53.0 | 40.0 | 65.0 | 21 | 53.0 | 40.0 | 65.0 | 42 | 53.0 | 34.0 | 69.0 | 22 | 53.5 | 47.0 | 58.0 | ||||||||||||||||||||||
| Dl CO/Va, % pred | 85 | 79.0 | 59.5 | 94.0 | 21 | 70.0 | 54.0 | 80.0 | 42 | 81.0 | 55.0 | 98.0 | 22 | 83.5 | 76.0 | 94.0 | ||||||||||||||||||||||
| Resting PaO2 , mm Hg | 83 | 61.0 | 54.0 | 70.0 | 21 | 64.0 | 53.0 | 71.0 | 40 | 59.0 | 53.0 | 65.0 | 22 | 65.5 | 59.0 | 70.0 | ||||||||||||||||||||||
| Resting aaPo 2, mm Hg | x | 83 | 17.2 | 10.5 | 23.6 | 21 | 16.0 | 9.9 | 19.0 | 40 | 21.2 | 14.4 | 29.5 | 22 | 13.4 | 9.5 | 19.0 | |||||||||||||||||||||
| Multistage V˙ o 2, % pred | 56 | 56.5 | 43.0 | 71.5 | 12 | 62.0 | 44.0 | 68.0 | 26 | 48.5 | 43.0 | 70.0 | 18 | 66.0 | 43.0 | 77.0 | ||||||||||||||||||||||
| Multistage PaO2 mm Hg | 54 | 52.0 | 45.0 | 55.8 | 12 | 52.5 | 46.2 | 55.9 | 25 | 49.6 | 43.8 | 55.8 | 17 | 51.0 | 46.0 | 55.7 | ||||||||||||||||||||||
| Multistage, aaPo 2,mm Hg | 54 | 36.3 | 29.5 | 42.0 | 12 | 38.2 | 33.3 | 41.1 | 25 | 35.0 | 27.7 | 43.6 | 17 | 35.8 | 27.8 | 41.2 | ||||||||||||||||||||||
All patients underwent open thoracotomy or video-assisted thoracoscopic lung biopsy. The method for collection, processing, and review of the pathologic specimens has been previously described (9, 10). Tissue was obtained from two sites, the upper and lower lobes of the same lung (when technically feasible). Immediately after the biopsy, all specimens were gently inflated with formalin, using a syringe and needle and injecting through the pleura. The specimens were then processed in routine fashion, and multiple-step sections showing representative pathology, as selected by one observer (J.W.), were cut and distributed among the four pathologists. Each pathologist received five slides from each block recut. The pathologists were unaware of the clinical, radiologic, or physiologic findings. Cases in which there were differing diagnoses were reevaluated by the pathology panel at periodic meetings and a consensus diagnosis was agreed upon. The 87 patients in whom there was a consensus for the diagnosis of UIP formed the basis of this study (7, 9, 12). Patients whose histopathologic findings were consistent with the following patterns were excluded from this analysis: nonspecific interstitial pneumonia (NSIP), desquamative interstitial pneumonia (DIP), respiratory bronchiolitis associated with ILD (RBILD), lymphoid interstitial pneumonia (LIP), acute interstitial pneumonia (AIP, diffuse alveolar damage), eosinophilic granuloma, hypersensitivity pneumonitis, sarcoidosis, or idiopathic bronchiolitis obliterans organizing pneumonia (idiopathic BOOP).
For each patient, the four pathologists (JW, TC, AF, and WT) performed a semiquantitative assessment of inflammatory/exudative changes, fibrotic/reparative changes, and airway alterations, in addition to an overall assessment of cellularity and fibrosis (see Table 4) (9). For each patient, the four pathologists graded 14 specific histopathologic features from slides stained with (1) hematoxylin-eosin, (2) pentachrome (which provided differential staining of elastic tissue, collagenized connective tissue, and mucopolysaccharide-rich stroma), (3) prussian blue (for iron), and (4) toludine blue. The parameters, which were scored in a semiquantitative fashion, included inflammatory/exudative changes, fibrotic/reparative changes, and airway alterations. A grade of zero to 5 was applied to (1) the extent and (2) the severity of cellularity in the alveolar wall (interstitium); (3) metaplastic cells lining the air spaces, including foci of honeycomb lung; (4) the extent and (5) the severity of cellularity in the alveolar space (so-called “desquamation”); (6) interstitial “young connective tissue,” i.e., rich in fibroblasts and metachromatic stroma, and relatively poor in mature collagen in the small airways; (7) interstitial fibrosis (including the percent of lung involved by honeycomb cysts, and foci with young connective tissue); (8) honeycomb cysts; (9) metaplastic smooth muscle in the stroma (as distinct from normal smooth muscle associated with airways and vasculature); (10) myointimal mural thickening in the vessel walls. In addition, a score of zero to 2 (absent = 0; present = 1; marked = 2) was used to assess (11) small airway lumenal granulation tissue; (12) intraalveolar granulation tissue; (13) airway wall inflammation; and (14) airway wall fibrosis.
| 95% CI | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Variable | (n) | Risk Ratio† | Lower | Upper | p Value | |||||
| Cellularity factor | 86 | 1.15 | 0.93 | 1.43 | 0.2072 | |||||
| Cellular infiltration of the alveolar walls, extent | 87 | 1.10 | 0.78 | 1.55 | 0.6067 | |||||
| Cellular infiltration of the alveolar walls, severity | 87 | N/A | N/A | N/A | 0.2469 | |||||
| Alveolar Space Cellularity Factor (“desquamation”) | 86 | 0.91 | 0.75 | 1.11 | 0.3449 | |||||
| Alveolar space cellularity, extent | 87 | 1.12 | 0.82 | 1.55 | 0.4602 | |||||
| Alveolar space cellularity, severity | 86 | 0.79 | 0.52 | 1.18 | 0.2476 | |||||
| Fibrotic/reparative factor | 85 | 1.00 | 0.93 | 1.07 | 0.8921 | |||||
| Alveolar wall cell metaplasia | 87 | 0.88 | 0.64 | 1.21 | 0.4379 | |||||
| Interstitial fibrosis | 86 | 0.99 | 0.73 | 1.35 | 0.9432 | |||||
| Honeycomb cysts | 87 | 1.00 | 0.79 | 1.28 | 0.9820 | |||||
| Metaplastic smooth muscle in the stroma | 87 | 0.87 | 0.67 | 1.12 | 0.2697 | |||||
| Myointimal mural thickening in the vessel walls | 86 | 1.08 | 0.81 | 1.42 | 0.6064 | |||||
| Granulation/connective tissue factor | 84 | 1.74 | 1.31 | 2.33 | 0.0002 | |||||
| Alveolar space granulation tissue, extent | 87 | N/A | N/A | N/A | 0.0367 | |||||
| Airway lumenal granulation tissue, extent | 87 | 0.89 | 0.26 | 3.03 | 0.8498 | |||||
| Interstitial “young connective tissue” | 86 | 1.93 | 1.31 | 2.83 | 0.0009 | |||||
| Total pathology | 86 | 0.99 | 0.95 | 1.04 | 0.7332 | |||||
As previously described (9), the principal component factor analysis of the means of the ratings of the four pathologists for each of these histologic features resulted in derivation of four factor scores:
1. The fibrosis factor (maximum score = 25), which is composed of interstitial fibrosis, honeycomb cysts, alveolar wall metaplastic cells lining the air spaces, metaplastic smooth muscle in the stroma, and myointimal mural thickening in the vessel walls.
2. The cellularity factor (maximum score = 10), which is composed of the severity and extent of cellular infiltration of the alveolar walls.
3. The alveolar space cellularity factor (maximum score = 10), which is composed of the severity and extent of cellularity within the alveolar space.
4. The granulation and young connective tissue factor (maximum score = 9), which comprises interstitial “young connective tissue” and granulation tissue in the lumens of small airways and alveoli.
Each factor score was derived from the sum of the scores assigned to its components, and the total pathology score was derived from the sum of the four factor scores. The maximum total pathology score was 54.
At entry, most patients had never received treatment directed at IPF (n = 62, 71% of patients); 12 (14%) were not receiving treatment at the time of lung biopsy but had been receiving short courses of corticosteroid treatment more than 30 d prior to the lung biopsy; 13 (15%) had been treated within 30 d of the biopsy. None of the patients had received significant doses of corticosteroid therapy (defined as a total of 2,700 mg of prednisone in any 90-d period) before diagnosis and entry into the study.
Patients were considered censored if they (1) were still alive when last contacted (censored at the last status date), (2) had received a lung transplant (censored at the time of the transplant), or (3) died from a cause other than ILD (censored at the expiration date). Survival time was calculated as the time since surgical lung biopsy.
The Kruskal-Wallis test was used to compare the three smoking groups for the continuous variables of interest, followed by pairwise comparisons using Wilcoxon's rank sum test. Dichotomous variables were compared using chi-square tests. Fisher's protected method was used to correct for multiple comparisons. Pathology variables were dichotomized (for plots only) by considering values below the median to be “low” and those above the median to be “high.”
The survival function was estimated using the Kaplan-Meier method (15). Estimates of the survival function were stratified by smoking status and the four pathology factors. The log-rank statistic was used to compare survival among groups (15). The effect of each variable on the risk of death after controlling for age, sex, and smoking status was modeled using Cox proportional hazards regression (15). Risk ratios are reported for these analyses. Influential points were identified through the use of the likelihood displacement and lmax statistics (16). Patients who accounted for more than 10 times the expected variability of the elements of the lmax statistic or had an likelihood displacement statistic of 0.5 or greater were excluded from the statistical analysis. Points that were considered influential were excluded from the Cox proportional hazards regression analyses. Multivariable models were developed on the subset of patients with complete data for the variables of interest. Akaike's Information Criteria (AIC) (17) was used to compare the multivariable models.
Descriptive statistics were generated using JMP statistical software (SAS Institute Inc., Cary, NC). All other statistical analysis was performed using the SAS statistical package (SAS). Unless otherwise noted, all tests were two-sided and performed at the 0.05 significance level.
At the time of the initial visit, the median time that patients had experienced shortness of breath was 24 mo. The duration of symptoms was not affected by smoking status. The median length of follow-up from the onset of symptoms was 65 mo; current smokers had the longest duration of follow-up (94 mo). The median length of follow-up from the time of the biopsy was 40 mo, with longest follow-up time in the current smoker group (63 mo) and the shortest follow-up time in the former smokers group (32 mo). Survival was assessed through September 30, 1999.
After entry into the study, 80 subjects received treatment for their illness with immunosuppressive or cytotoxic therapy: 44 received prednisone alone (one received prednisolone only intravenously); three received cyclophosphamide alone; 26 received prednisone and cyclophosphamide; five received prednisone, cyclophosphamide, and colchicine; one each received prednisone and colchicine, or cyclophosphamide and colchicine. Seven patients received no treatment.
Sixty-three patients (72%) died during the study period. In the analysis, we censored those patients who died because of an illness other than IPF (n = 6) or underwent lung transplantation (n = 4). The median survival time for all subjects was 47.5 mo (95% CI: 33.4–73.4) from the time of lung biopsy. There was a tendency for a greater risk of death for men (approximately 47% greater risk than for women, p = 0.18) and patients with older age (p = 0.0667). The age, sex, and smoking-adjusted survival analysis for the individual clinical and physiologic variables are shown in Table 3. The patient's race (white versus nonwhite) and time since onset of symptoms were not significantly related to the risk of death. An increased risk of death was associated with the number of pack-years of smoking (p = 0.0218) and the degree of dyspnea (p = 0.0029), with a one-unit increase in the dyspnea score being associated with a 10% increase in the risk of death. Vtg, TLC, FVC, FEV1, SGaw, the log of the K value, coefficient of retraction, Dl CO, and PaO2 at maximal exercise were significantly related to survival (Table 3). Patients with more normal PaO2 at the end of maximal exercise survived longer (p = 0.0057). The Kaplan-Meier survival estimates stratified by smoking status are shown in Figure 1.
| 95% CI | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Variable | (n) | Risk Ratio* | Lower | Upper | p Value | |||||
| Race, nonwhite vs. white | 86 | 1.53 | 0.541 | 4.357 | 0.4208 | |||||
| Pack-years of cigarette smoking | 85 | 1.01 | 1.002 | 1.023 | 0.0218 | |||||
| Mo since onset of symptoms | 84 | 1.00 | 0.992 | 1.011 | 0.7208 | |||||
| Dyspnea, scale 0 to 20 | 86 | 1.10 | 1.033 | 1.171 | 0.0029 | |||||
| Vtg, % pred | 85 | 0.96 | 0.945 | 0.983 | 0.0002 | |||||
| TLC, % pred | 86 | 0.96 | 0.940 | 0.981 | 0.0001 | |||||
| FVC, % pred | 87 | N/A | N/A | N/A | 0.0027 | |||||
| FEV1, % pred | 87 | N/A | N/A | N/A | 0.0193 | |||||
| SGaw, % pred | 82 | 1.01 | 1.004 | 1.019 | 0.0020 | |||||
| K value, log | 74 | 0.29 | 0.159 | 0.536 | 0.0001 | |||||
| Coefficient of retraction, cm H2O/L | 77 | 1.21 | 1.122 | 1.313 | < 0.0001 | |||||
| Dl CO, % pred | 84 | 0.97 | 0.952 | 0.990 | 0.0028 | |||||
| Dl CO/Va, % pred | 85 | 0.99 | 0.981 | 1.007 | 0.3703 | |||||
| Resting PaO2 , mm Hg | 83 | 0.98 | 0.954 | 1.007 | 0.1505 | |||||
| Resting aaPo 2, mm Hg | 83 | 1.03 | 0.999 | 1.059 | 0.0596 | |||||
| Multistage PaO2 , mm Hg | 52 | 0.93 | 0.891 | 0.980 | 0.0057 | |||||
| Multistage aaPo 2, mm Hg | 54 | 1.04 | 0.990 | 1.084 | 0.1291 | |||||
| Multistage percent predicted V˙ o 2 | 56 | N/A | N/A | N/A | 0.5999 | |||||
Fig. 1. Kaplan-Meier survival analysis grouped by smoking status at entry into the study. A better survival was seen in current smokers compared with former or never smokers (n = 87, p = 0.0022), with current smokers having the longest median survival time (83.2 mo), followed by never and former smokers (65.8 compared with 32.1 mo, respectively).
[More] [Minimize]A wide range of pathology factor scores was observed in our patients with UIP. The median score for each factor score for the entire group was: cellularity, 6.3 (25th, 75th percentile; 5.5–7.1); alveolar space cellularity, 4.5 (3.5–5.5); fibrosis, 12.9 (9.8– 16.5); granulation/connective tissue, 1.8 (1.0–2.7); and total pathology score, 26.0 (22.3–30.8). Current smokers had significantly lower degrees of cellularity and granulation/connective tissue and higher alveolar space cellularity than did former and never smokers (Figure 2). The amount of fibrosis did not differ by smoking status.
Fig. 2. Influence of cigarette smoking on the histopathologic findings in patients with IPF. (A). Current smokers have lesser degrees of cellularity (p < 0.05). (B). Current smokers have a slightly higher degree of alveolar space cellularity (p = NS). (C ). The degree of fibrosis is similar in all groups (p = NS). (D). Current smokers have less granulation/young connective tissue abnormalities (p < 0.05).
In the age-, sex-, and smoking-adjusted survival analyses, only the granulation/connective tissue score was a significant predictor of survival in patients with IPF (Table 4). A one-unit increase in the granulation/connective tissue factor was associated with a 1.74-fold greater risk of death. Of the specific components that comprise this factor, the degree of alveolar space granulation tissue and the fibrotic/reparative changes in young connective tissue were each significantly associated with survival. A one grade level increase of fibrotic/reparative changes in young connective tissue increases the risk of death almost twofold. On the other hand, the airway lumenal granulation tissue extent of involvement was not associated with an increased risk of death. The Kaplan-Meier survival analysis for each factor score dichotomized at the median for entire group is shown in Figure 3.
Fig. 3. Kaplan-Meier survival analysis grouped by dichotomized factor score at the median for entire group. (A). Cellularity: Survival tended to be longer in subjects with less cellularity (Low: ranges of score 2.25 to 6.25; median survival, 59.2 mo; High: range of score 6.4 to 9.25; median survival, 36.2 mo; p = 0.46). (B). Alveolar space cellularity: Survival tended to be better in subjects with greater degrees of alveolar space cellularity (Low : ranges of score 1.5 to 4.5; median survival, 36.2 mo; High: range of score 4.6 to 7.5; median survival, 73.4 mo; p = 0.19). (C ). Fibrosis: Survival was not different in the two groups (Low : range of score, 1.6 to 12.9; median survival, 49.6 mo; High: range of score, 13.0 to 24.8; median survival, 43.4 mo; p = 0.98). (D) Granulation/connective tissue: Survival was better in subjects with lesser degrees of granulation/connective tissue (Low: range of score, 0 to 1.8; median survival, 65.8 mo; High: range of score, 2.0 to 5.5; median survival, 22.8 mo; p = 0.002).
Multivariable survival model. Multiple independent variables were studied in Cox proportional hazards models to assess survival (Table 5). The importance of the multivariable analysis is that it allows identification of those manifestations that are independently and significantly related to outcome (survival) while controlling for the other factors in the model. Age, sex, level of dyspnea, smoking status, TLC, Dl CO, coefficient of retraction, and the four pathology factors were included in the multivariable model. FVC and Vtg were excluded since they strongly correlated with TLC (0.82 and 0.76, respectively). Dyspnea, coefficient of retraction, and granulation/connective tissue factor, were significantly related to the risk of death. In this model, current smokers had a 22% greater risk of death than did never smokers and former smokers had an 88% greater risk of death than did never smokers. A change in two levels on our dyspnea scale results in a 49% increased risk of death. An increase of one grade of the granulation tissue factor is associated with a two-fold risk of death.
| 95% CI | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Variable | Unit of Change | Risk Ratio | Lower | Upper | p Value* | |||||
| Age at time of lung biopsy | 5 yr | 1.029 | 0.877 | 1.207 | 0.7281 | |||||
| Sex, Male/Female | N/A | 1.704 | 0.836 | 3.476 | 0.1425 | |||||
| Smoker, Current (compared to Never) | N/A | 1.221 | 0.353 | 4.222 | 0.7527 | |||||
| Smoker, Former (compared to Never) | N/A | 1.881 | 0.840 | 4.215 | 0.1247 | |||||
| Dyspnea Scale, 0–20 | 4 units | 1.490 | 1.093 | 2.031 | 0.0117 | |||||
| Coefficient of Retraction | 0.5 cm H20/L | 1.118 | 1.070 | 1.167 | < 0.0001 | |||||
| Granulation/Connective Tissue Factor | 1 unit | 2.067 | 1.438 | 2.972 | < 0.0001 | |||||
The objective of this study was to determine whether or not specific histopathologic features of UIP predicted survival in patients with IPF. We prospectively evaluated the largest number of untreated, surgical lung biopsy-proven, cases of IPF reported to date (7). In addition, the present study provided an improved method of grading the degree of cellularity and fibrosis (9, 11). We found that the extent of granulation/connective tissue present on lung tissue examination was the only histopathologic feature predictive of survival in IPF. By contrast, the extent and severity of interstitial fibrosis or cellularity on lung biopsy were not predictive of survival. A history of cigarette smoking, the level of dyspnea, and the degree of lung stiffness at presentation were also shown to be independent factors predicting survival in this population.
Previous correlative studies of outcome and histopathology have shown that prognosis and response to therapy in the idiopathic interstitial pneumonias (IIPs) was determined by the extent of interstitial fibrosis and cellularity on biopsy (8). However, this widely held view that predominantly “cellular” biopsies in patients with IPF are associated with a greater likelihood of response to corticosteroids and a better prognosis appears to have little support (1, 7). First, most studies involved a small number of cases of IPF. Second, the pathologic findings were often assessed from tissue samples obtained by percutaneous needle or transbronchial rather than from surgical lung biopsy specimens. Histopathologic confirmation of UIP and grading of specific features is difficult in the small lung biopsy specimens obtained by these methods (1, 7). Third, it is now recognized that histopathologic subtypes other than UIP were commonly included among the patients evaluated in these studies (e.g., DIP, RB-ILD, NSIP, and idiopathic BOOP) (1, 18, 19). These are distinct clinical, radiographic, and histopathologic entities with different responses to therapy and survival rates. Importantly, data show that the UIP pattern is associated with a substantially worse survival than other chronic IIPs (1, 18, 19). Fourth, no single histologic finding, other than end-stage fibrosis and honeycombing, has been shown to correlate with treatment response or prognosis in UIP (7). A positive correlation between the extent of overall cellularity, or a negative correlation with the extent of fibrosis, has been shown to correlate with responsiveness to corticosteroid therapy (3, 8, 20-27). Fifth, the term “cellularity” was used indiscriminately for interstitial inflammation, intraalveolar macrophage accumulation, or a combination of both. Sixth, the term “fibrosis” has included all manner of fibroblastic proliferation and collagen deposition. More recently, a distinction has been made between fibrotic areas of the lesion characterized by “old,” relatively acellular collagen bundles and small aggregates of fibroblasts in myxoid connective tissue, so-called “fibroblastic foci” (1, 7). Until the present study, the relative roles of the stage of fibrosis (mature collagen versus fibroblast foci) in determining prognosis had not been examined (7).
In IPF, it is hypothesized that early stages of the disease involve less of the lung and is characterized predominantly by cellularity and minimal fibrosis, whereas in advanced disease a large number of alveoli are destroyed by fibrosis with varying degrees of cellularity. This hypothesis has been challenged and it has been proposed that the earliest changes in UIP are fibroblastic foci, a manifestation of ongoing lung injury (7). In this study, a distinction was made between interstitial fibrosis with extensive collagen deposition (which includes honeycomb change) and fibroblastic foci recognized as young connective tissue or connective tissue with granulation tissue type appearance. We have shown that when individual pathologic variables were assessed and quantified, only the granulation/connective tissue factor score was a significant predictor of survival time in patients with IPF. Moreover, the specific features that predicted survival were the degree of alveolar space granulation tissue deposition and extent of young connective tissue present within the fibroblastic foci. Interestingly, when this form of connective tissue appears as an air space process in conditions such as bronchiolitis obliterans organizing pneumonia, it appears to be potentially reversible. However, when identified in IPF, this form of connective tissue has a detrimental impact on prognosis. On the other hand, the extent and severity of interstitial cellularity, alveolar space cellularity, or fibrosis did not predict survival. In fact, it appears that the interstitial inflammation and intraalveolar macrophage accumulation (“desquamation”) are most likely secondary events (7).
These findings support the hypothesis that the critical pathway to end-stage fibrosis is not “alveolitis” but rather the apparently ongoing epithelial damage and repair process associated with persistent fibroblastic proliferation. Recent experimental data support an important role for fibroblastic proliferation in the lung injury and repair process in pulmonary fibrosis. It has been proposed that incomplete or delayed alveolar repair after lung injury leads to an acceleration of collagen deposition and lung fibroblast proliferation. Fibroblasts isolated from fibrotic lung induce apoptosis of alveolar epithelial cells in vitro (28). Further, epithelial cell death is most prominent immediately adjacent to underlying foci of fibroblasts (29). These data suggest that the epithelium of the fibrotic lung contain dying and proliferating cells and that alveolar epithelial cell death is induced by abnormal lung fibroblasts (29). Thus, controlling the fibrogenesis (evident in the regions of fibroblastic foci), rather than the “alveolitis,” appears most important in arresting the progressive disease and preventing the fatal outcome so common in IPF.
Many studies have shown a high percentage of ever cigarette smokers among persons with IPF (3, 4, 20, 30) and case control studies suggest that smoking is a risk factor for the development of IPF (31-33). However, earlier studies showed that being an ever smoker did not affect survival in IPF (3, 4, 34, 35). In the present study, smoking status at the time of biopsy was a significant prognostic variable in that current smokers had a markedly improved survival compared with never or former smokers.
Interestingly, not only does cigarette smoking play a role in the development of IPF (33) and alters lung function (2, 11), it also alters the histopathologic appearance of the disease. We found that current smokers have less overall interstitial cellularity but greater alveolar space inflammation—likely reflecting increased inflammation secondary to ongoing accumulation of macrophages as a result of smoking. The fibrotic changes were similar among the current, former, and never smoker groups; however, there were significantly lower granulation/connective tissue scores among the current smokers. There were no differences in any of the pathology factor scores between never and former smokers. It is probably the decreased granulation/connective tissue that is responsible for the longer survival in current smokers. Conversely, some factor in cigarette smoke may be contributing to decrease granulation/connective tissue. However, multivariable model suggests that if the other factors in the model were held constant (for example, granulation/connective tissue, dyspnea, and coefficient of retraction), current smokers and former smokers would tend to have an increased risk of death as opposed to never smokers. However, this difference is not statistically significant. These findings suggest that the ongoing epithelial damage and repair processes associated with persistent fibroblastic proliferation is less among current smokers.
The current literature argues that in the absence of a surgical (thoracoscopic or open) lung biopsy, the diagnosis of IPF remains uncertain. Further, the separation of the four distinct histologically forms of the IIPs (UIP, DIP, NSIP, AIP) is essential because these patterns differ in clinical presentations, responses to therapy, and clinical course. The present study has shown that careful analysis and quantification of the specific histopathologic features found in UIP is useful in defining the prognosis of patients with IPF. Somewhat surprisingly, the specific histopathologic features that predicted survival were the degree of alveolar space granulation tissue deposition and extent of young connective tissue present within the fibroblastic foci rather than the extent and severity of interstitial cellularity or fibrosis. The full implications of these findings remain to be determined. However, given the disappointing therapeutic results achieved with immunosuppressive or anti-inflammatory agents, these data suggest that future therapies should be aimed at preventing or inhibiting the fibroproliferative response.
The writers thank Drs. L.C. Watters, T.L. Dunn, A. Shen, and R.L. Mortenson for their role in enrolling patients; Alma (Dolly) Kervitsky, S. Arlene Niccoli, Martin Wallace, Trudy McDermott, and Janet Henson for their technical assistance; Becki Bucher Bartelson for her assistance with the data analysis; William Kastner and David Ikle for the design and maintenance of the computerized data for the ILD study; the referring physicians; and a special thanks to the patients for allowing the investigators to participate in their care. We would like to remember and express our appreciation to the late William (Whitey) Thurlbeck for his contributions to this and other studies.
Supported by a SCOR Grant No. HL-27353 from the National Heart, Lung and Blood Institute.
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