American Journal of Respiratory and Critical Care Medicine

Background: In 2002 the American Thoracic Society/European Respiratory Society (ATS/ERS) classification of idiopathic interstitial pneumonias (IIPs) defined seven specific entities, and provided standardized terminology and diagnostic criteria. In addition, the historical “gold standard” of histologic diagnosis was replaced by a multidisciplinary approach. Since 2002 many publications have provided new information about IIPs.

Purpose: The objective of this statement is to update the 2002 ATS/ERS classification of IIPs.

Methods: An international multidisciplinary panel was formed and developed key questions that were addressed through a review of the literature published between 2000 and 2011.

Results: Substantial progress has been made in IIPs since the previous classification. Nonspecific interstitial pneumonia is now better defined. Respiratory bronchiolitis–interstitial lung disease is now commonly diagnosed without surgical biopsy. The clinical course of idiopathic pulmonary fibrosis and nonspecific interstitial pneumonia is recognized to be heterogeneous. Acute exacerbation of IIPs is now well defined. A substantial percentage of patients with IIP are difficult to classify, often due to mixed patterns of lung injury. A classification based on observed disease behavior is proposed for patients who are difficult to classify or for entities with heterogeneity in clinical course. A group of rare entities, including pleuroparenchymal fibroelastosis and rare histologic patterns, is introduced. The rapidly evolving field of molecular markers is reviewed with the intent of promoting additional investigations that may help in determining diagnosis, and potentially prognosis and treatment.

Conclusions: This update is a supplement to the previous 2002 IIP classification document. It outlines advances in the past decade and potential areas for future investigation.

Executive Summary



Summary of Major Revisions of the IIP Classification

General Progress in IIPs since 2002

 Multidisciplinary Approach

 Observer Agreement in Diagnosis of IIP

Important Differential Diagnostic Considerations

 Hypersensitivity Pneumonitis

 Collagen Vascular Disease

 Familial Interstitial Pneumonia

 Coexisting Patterns

Progress in Specific IIPs since 2002

 Chronic Fibrosing IIPs

 Smoking-related IIPs

 Acute or Subacute IIPs

Rare IIPs

 Idiopathic Lymphocytic Interstitial Pneumonia

 Idiopathic Pleuroparenchymal Fibroelastosis

Rare Histologic Patterns

 Acute Fibrinous and Organizing Pneumonia

 Bronchiolocentric patterns of interstitial pneumonia

Unclassifiable IIP

Clinical Classification of Disease Behavior


There are several specific areas that are given special attention in this revision of the 2002 American Thoracic Society/European Respiratory Society idiopathic interstitial pneumonia (IIP) statement.


Idiopathic nonspecific interstitial pneumonia (NSIP) is now accepted as a specific clinicopathologic entity. It has become evident that clinical progression is highly heterogeneous, with several studies suggesting that a subset of patients demonstrate progression to end-stage fibrosis; criteria to define this group at the time of diagnosis would be helpful.


New information has accumulated on smoking-related interstitial lung disease, including patients with combined emphysema and interstitial fibrosis. In clinical practice, respiratory bronchiolitis–interstitial lung disease is increasingly diagnosed without surgical lung biopsy in smokers on the basis of clinical and imaging features (ground-glass opacities and centrilobular nodules) and bronchoalveolar lavage (smoker’s macrophages and absence of lymphocytosis).


The natural progression of idiopathic pulmonary fibrosis (IPF) is acknowledged to be heterogeneous with some patients remaining stable for prolonged periods, others showing more rapid steady progression, and still others succumbing to acute exacerbation.


Acute exacerbation is better defined and recognized to occur in chronic fibrosing IIPs (IPF and NSIP).


Some patients with IIP are difficult to classify, often because of mixed patterns of lung injury.


It is recognized that there is a need to provide a clinical algorithm for classifying and managing IIP cases. This is particularly applicable when no biopsy is available and high-resolution computed tomography is not diagnostic.


Pleuroparenchymal fibroelastosis is recognized as a specific rare entity, usually idiopathic. Other less well-defined histologic patterns, such as bronchiolocentric inflammation and fibrosis, are also included.


A rapidly emerging field of molecular markers holds promise for improving diagnostic approaches. These markers may also be useful in predicting prognosis and response to different therapies. Incorporation of genetic and molecular studies may revolutionize the approach to diagnosis and classification of the IIPs.

The objective of this statement is to update the 2002 American Thoracic Society/European Respiratory Society (ATS/ERS) classification of idiopathic interstitial pneumonias (IIPs) (1). Focus is placed on describing changes to previously described clinical entities, describing new clinical entities, and describing new histologic patterns. This update is not intended as a stand-alone document and should be used as a supplement to the original 2002 IIP classification. In 2002, the ATS/ERS IIP classification (1) defined seven disease categories, and proposed standardized terminology and diagnostic criteria. In addition, the historical “gold standard” of histologic diagnosis was replaced by a “dynamic integrated approach” using multidisciplinary discussion (MDD). The 2002 IIP classification was used in 75% (157 of 208) of all clinical publications on the topic of IIPs between 2004 and 2011. The new information from these publications is incorporated in this update.

This project was performed under supervision by the ATS Documents Development and Implementation Committee in collaboration with the ERS (Table E1 in the online supplement). An international multidisciplinary panel was assembled. The panel consisted of 34 experts in interstitial lung diseases (19 pulmonologists, 4 radiologists, 5 pathologists, 2 experts in evidence-based medicine, and 4 molecular biologists). Several meetings were held by members of the international multidisciplinary panel (Table E2), who disclosed conflicts of interest, which were vetted according to ATS and ERS policies.

Key questions were developed that the committee believed important for the classification of IIPs (see Appendix 1 in the online supplement). A literature search was performed to identify new publications that pertained to these key questions, assisted by two librarians experienced in literature searches for pulmonary diseases. Literature retrieved from Medline searches between 2000 and 2011 was used to produce this statement.

The committee was divided into subgroups assigned to specific sections of the document. These subgroups reviewed the relevant literature and produced the first draft of their respective sections. These sections were compiled by the committee chair and a complete first draft was edited by the writing subcommittee. This document was reviewed and edited by all committee members before final review by the writing subcommittee. The revised document was approved by all authors.

In the revision of the IIP classification, the main entities are preserved (Table 1). However, there are several important changes. First, cryptogenic fibrosing alveolitis is removed, leaving idiopathic pulmonary fibrosis (IPF) as the sole clinical term for this diagnosis. Second, idiopathic nonspecific interstitial pneumonia (NSIP) is now accepted as a distinct clinical entity with removal of the term “provisional” (2). Third, major IIPs are distinguished from rare IIPs and unclassifiable cases. Fourth, rare histologic patterns of acute fibrinous and organizing pneumonia (AFOP) and interstitial pneumonias with a bronchiolocentric distribution are recognized. Fifth, the major IIPs are grouped into chronic fibrosing (IPF and NSIP; Figures 1 and 2), smoking-related (respiratory bronchiolitis–interstitial lung disease [RB-ILD] and desquamative interstitial pneumonia [DIP]; Figure 3), and acute/subacute IIPs (cryptogenic organizing pneumonia [COP] and acute interstitial pneumonia [AIP]; Figure 4 and Table 2). Sixth, a clinical disease behavior classification is proposed. Last, molecular and genetic features are reviewed.


Major idiopathic interstitial pneumonias
 Idiopathic pulmonary fibrosis
 Idiopathic nonspecific interstitial pneumonia
 Respiratory bronchiolitis–interstitial lung disease
 Desquamative interstitial pneumonia
 Cryptogenic organizing pneumonia
 Acute interstitial pneumonia
Rare idiopathic interstitial pneumonias
 Idiopathic lymphoid interstitial pneumonia
 Idiopathic pleuroparenchymal fibroelastosis
Unclassifiable idiopathic interstitial pneumonias*

*Causes of unclassifiable idiopathic interstitial pneumonia include (1) inadequate clinical, radiologic, or pathologic data and (2) major discordance between clinical, radiologic, and pathologic findings that may occur in the following situations: (a) previous therapy resulting in substantial alteration of radiologic or histologic findings (e.g., biopsy of desquamative interstitial pneumonia after steroid therapy, which shows only residual nonspecific interstitial pneumonia [153]); (b) new entity, or unusual variant of recognized entity, not adequately characterized by the current American Thoracic Society/European Respiratory Society classification (e.g., variant of organizing pneumonia with supervening fibrosis) (79); and (c) multiple high-resolution computed tomography and/or pathologic patterns that may be encountered in patients with idiopathic interstitial pneumonia.


CategoryClinical–Radiologic–Pathologic DiagnosesAssociated Radiologic and/or Pathologic–Morphologic Patterns
Chronic fibrosing IPIdiopathic pulmonary fibrosisUsual interstitial pneumonia
Idiopathic nonspecific interstitial pneumoniaNonspecific interstitial pneumonia
Smoking-related IP*Respiratory bronchiolitis-interstitial lung diseaseRespiratory bronchiolitis
Desquamative interstitial pneumoniaDesquamative interstitial pneumonia
Acute/subacute IPCryptogenic organizing pneumoniaOrganizing pneumonia
Acute interstitial pneumoniaDiffuse alveolar damage

Definition of abbreviation: IP = interstitial pneumonia.

*Desquamative interstitial pneumonia can occasionally occur in nonsmokers.

Multidisciplinary Approach

The process of achieving a multidisciplinary diagnosis in a patient with IIP is dynamic, requiring close communication between clinician, radiologist, and when appropriate, pathologist (1). Clinical data (presentation, exposures, smoking status, associated diseases, lung function, laboratory findings) and radiologic findings are essential for multidisciplinary diagnosis.

The multidisciplinary approach does not lessen the importance of lung biopsy in the diagnosis of IIPs; rather, it defines the settings where biopsy is more informative than high-resolution computed tomography (HRCT) and those where biopsy is not needed. Also, once a pathologist has recognized a histologic pattern (e.g., NSIP or organizing pneumonia [OP]), the clinician should reconsider potential causes (e.g., hypersensitivity pneumonitis [HP], collagen vascular disease [CVD], and drug exposure).

The diagnosis of IIPs requires exclusion of known causes of interstitial lung disease such as drug or inhalational exposure and CVD. Despite the known association of smoking with RB-ILD and DIP, these disorders were included in the classification in 2002 and they are maintained in this revision.

Observer Agreement in Diagnosis of IIP

Observer agreement is dependent on observer experience and the integration of data from all modalities. In early series, observer agreement was marginal among clinicians, radiologists, and pathologists (35). However, agreement between radiologists and pathologists has improved substantially with accumulated experience (6) and, especially, with integration of clinical data in a multidisciplinary conference (4, 7). Academic physicians in a multidisciplinary setting have better diagnostic agreement than community physicians, who are more likely to assign the diagnosis of IPF (7). These data underline the need for patient evaluation in regional centers using multidisciplinary evaluation (7, 8).

Hypersensitivity Pneumonitis

IIPs are frequently confused with HP, and vice versa, except when the exposure is readily apparent. The ATS workshop on NSIP showed that MDD is particularly important in distinguishing HP from NSIP (2). In the past 10 years, the clinical (9), HRCT (1012), and pathologic (1315) features of chronic HP have been more sharply defined, helping to separate these cases from the IIPs, particularly IPF and NSIP (9, 1116). HRCT findings suggesting HP include centrilobular nodules, mosaic air-trapping, and upper lobe distribution (Figures 5A and 5B) (11, 12). Biopsy findings suggesting HP include bronchiolocentric distribution and poorly formed granulomas (Figures 5C and 5D) (1315). A detailed search for potential exposure in patients with these findings is essential, including consideration of specific circulating IgG antibodies, but up to 30% of subjects with histologic HP have no identifiable exposure (17, 18).

Collagen Vascular Disease

CVD is a frequent cause of interstitial pneumonia patterns, especially NSIP. Clinical, serologic, HRCT, and histologic findings may be helpful in distinguishing IIPs from ILD associated with CVD (1922). The extent of serologic evaluation to be performed in the evaluation of suspected IPF has been suggested previously (8). A substantial percentage of patients with NSIP have findings suggesting, but not meeting, criteria for a defined CVD (2325). However, these cases are still accepted as IIPs.

Familial Interstitial Pneumonia

IIPs have been reported in closely related family members in 2–20% of cases (2629). These cases remain classified as IIPs despite the genetic predisposition. Heterozygous mutations in SFTPC (∼1%), SFTPA2 (∼1%), TERT (∼15%), and TERC (∼1%) are responsible for about 20% of all familial interstitial pneumonias (FIPs) (2932). Sporadic IPF, in the absence of telomerase mutations, is often associated with telomere shortening, suggesting that pathways involved in familial disease may contribute to sporadic disease (3335). Most FIP families (80%) have evidence of vertical transmission suggesting single autosomal dominant mechanisms, but most responsible genes have not yet been identified. A recent genome-wide linkage scan showed that a common variant in the promoter of the MUCB gene is associated with the development of both familial and sporadic IPF. This result was confirmed in an independent cohort (36, 37).

Familial IIPs can be indistinguishable from nonfamilial cases on HRCT and lung biopsy. All patients with suspected IIP should therefore be questioned about relevant family history as this may guide gene mutation search, and management or evaluation of other family members (38).

Coexisting Patterns

Most patients with a chronic IIP can be given a single clinical–radiologic–pathologic diagnosis. However, multiple pathologic and/or HRCT patterns may be found in the same patient. Different patterns may be seen in a single biopsy or in biopsies from multiple sites (e.g., usual interstitial pneumonia [UIP] in one lobe and NSIP in another) (39), or when pathologic and HRCT patterns differ. In smokers, multiple HRCT and histologic features may coexist including Langerhans’ cell histiocytosis, respiratory bronchiolitis (RB), desquamative interstitial pneumonia (DIP), pulmonary fibrosis (UIP or NSIP), and emphysema (4042). Combined pulmonary fibrosis and emphysema (CPFE) is an example of coexisting patterns. CPFE comprises a heterogeneous population of patients, not believed to represent a distinctive IIP. Patients with CPFE have increased risk of developing pulmonary hypertension, which portends poor prognosis (4346). When coexisting patterns occur, MDD may determine the clinical significance of individual patterns (4, 47, 48).

Chronic Fibrosing IIPs
Idiopathic pulmonary fibrosis.

An updated evidence-based guideline for the diagnosis and management of IPF was recently published (8). A new diagnostic algorithm and schema for correlating histologic and radiologic findings in patients with suspected IPF was provided in this guideline (8). New aspects of this algorithm included criteria for three levels of certainty for patterns of UIP based on HRCT findings (UIP, possible UIP, and inconsistent with UIP) and four levels of certainty for pathologic diagnosis (UIP, probable, possible, and not UIP) (8). The diagnosis of IPF requires (1) exclusion of other known causes of ILD, (2) the presence of a UIP pattern on HRCT in patients not subjected to surgical lung biopsy (SLB), and (3) specific combinations of HRCT and SLB patterns in patients subjected to SLB (Figures 1A–1C).

Histologic UIP may be associated with atypical HRCT patterns (Figures 1A–1C) (8), including extensive ground-glass opacity, nodules, or mosaic attenuation, and after MDD some of these patients will be diagnosed with IPF (4952). Typical UIP HRCT pattern is illustrated elsewhere (1, 8). Patients with IPF and definite UIP by HRCT have shorter survival than those with indeterminate HRCT findings (49, 51, 53).

Idiopathic nonspecific interstitial pneumonia.

The diagnostic criteria for NSIP were summarized in a recent ATS workshop (2). On the basis of the analysis of cases and the available literature, this workshop recommended that NSIP be accepted as a distinct entity among the IIPs, with removal of the term “provisional.” Importantly, the NSIP pattern occurs not only as an idiopathic condition, but also in a variety of settings including CVD, HP, and drug toxicity, and in some patients with familial pulmonary fibrosis. MDD is especially important to establish the diagnosis of idiopathic NSIP (2).

The most common HRCT abnormality in NSIP is bilateral ground-glass opacity (Figures 2A and 2B) (26, 5462). Irregular reticular opacities with traction bronchiectasis and bronchiolectasis occur in approximately 75% of cases (2, 5462). Subpleural sparing may be helpful in distinguishing NSIP from UIP (2, 12, 52). Consolidation, if present, reflects an OP component and may suggest CVD. Honeycombing is sparse or absent at presentation but may increase in prevalence and extent during follow-up (63).

The histologic features include varying amounts of interstitial inflammation and fibrosis with a uniform appearance (Figures 2C and 2D) (2, 64, 65). Most cases of NSIP have a predominantly fibrotic pattern of injury with rare cases of isolated cellular NSIP (59, 62, 66). OP and honeycomb fibrosis should be inconspicuous or absent.

The prognosis is variable. Some patients improve, others remain stable or improve on treatment, but some evolve to end-stage fibrosis and eventually die of the disease (2, 63, 67).

Smoking-related IIPs

RB-ILD and desquamative interstitial pneumonia (DIP) represent a histologic spectrum of macrophage accumulation, with the distinction dependent on the extent and distribution of this process (and also reflected by the pattern of disease on HRCT). However, clinical presentation, imaging findings, and response to therapy differ and they remain classified separately. In the last decade, the term “smoking-related interstitial lung disease” has increasingly been used, encompassing most cases of DIP, and nearly all cases of RB-ILD and Langerhans’ cell histiocytosis (68, 69).

Respiratory bronchiolitis–interstitial lung disease.

Histologic RB is always present in current smokers (70) and can be viewed as a physiological response to smoking, which in a few individuals becomes extensive enough to result in an interstitial lung disease (RB-ILD). Characteristic HRCT features are ground-glass opacity and centrilobular nodules (Figures 3A and 3B). In clinical practice, RB-ILD is increasingly diagnosed without surgical lung biopsy in smokers with these HRCT findings and where bronchoalveolar lavage demonstrates smokers’ macrophages and the absence of lymphocytosis (potentially suggestive of HP in this setting, although HP is uncommon in smokers) (68, 71). The disease course is heterogeneous, with a significant minority having progression despite smoking cessation (72).

Desquamative interstitial pneumonia.

DIP has been recognized in nonsmokers (69), perhaps reflecting extension of childhood DIP into adult life (with the latter often due to surfactant protein [SP] gene mutations) (73, 74). Ten-year survival remains approximately 70%, with resistance to treatment in a significant minority.

Airspace enlargement with fibrosis.

DIP and RB-ILD need to be distinguished from the smoking-related changes including respiratory bronchiolitis and airspace enlargement with fibrosis (AEF) that have been described in the nonneoplastic lung parenchyma in lung cancer resection specimens (75, 76). These incidental HRCT and histologic findings in smokers are not regarded as a distinct form of IIP, but AEF shows more interstitial fibrosis than described in the classic definition of emphysema (77). AEF is an incidental histologic or HRCT finding, whereas patients with CPFE have clinically manifestations reflecting coexisting patterns of interstitial fibrosing and emphysema.

Acute or Subacute IIPs

IIPs may have an acute or subacute presentation, or an acute exacerbation may occur in a previously subclinical or unrecognized chronic IIP.

Cryptogenic organizing pneumonia.

COP continues to be included in the classification of IIP because of its idiopathic nature and the tendency on occasions to be confused with other forms of IIP, especially when there is progression to fibrosis. Because many cases are secondary, use of the generic term “OP” for this reaction pattern is suggested with modifiers as appropriate, for example, OP associated with rheumatoid arthritis.

Patients with COP typically present with a subacute illness of relatively short duration (median, less than 3 mo) with variable degrees of cough and dyspnea (7881). HRCT characteristically demonstrates patchy and often migratory consolidation in a subpleural, peribronchial, or bandlike pattern (Figures 4A–4D) (8284), commonly associated with ground-glass opacity (79, 83). Perilobular opacities and reversed halo (or atoll) sign (Figure 4C) may be helpful in suggesting the diagnosis (85, 86). Small unilateral or bilateral pleural effusion may occur in 10–30% of patients (83, 84, 86). The OP pattern is a patchy process characterized primarily by organizing pneumonia involving alveolar ducts and alveoli with or without bronchiolar intraluminal polyps. Some cases show more marked interstitial inflammation such that there is overlap with cellular NSIP.

The majority of patients recover completely with oral corticosteroids, but relapse is common (2, 78, 87). Sporadic reports have identified a subgroup of patients with OP that does not completely resolve despite prolonged treatment. Some of these cases are characterized by residual or progressive interstitial fibrosis, with or without recurrent episodes of OP (79, 88, 89). It is likely that some patients reported with fibrotic NSIP fall into this subgroup of patients with a fibrosing variant of OP. In such patients consolidation is prominent on HRCT, variably associated with reticular abnormalities. Some patients with this pattern of mixed fibrosis and organizing pneumonia are found to have underlying polymyositis or antisynthetase syndrome (90).

Acute interstitial pneumonia.

AIP is a distinct IIP characterized by rapidly progressive hypoxemia, mortality of 50% or more, and no proven treatment. Survivors usually have a good long-term prognosis (similar to adult respiratory distress syndrome [ARDS] survivors) but some experience recurrences or chronic, progressive interstitial lung disease (9193). AIP is idiopathic and should be distinguished from ARDS with known cause.

In the early, exudative phase of AIP, HRCT shows bilateral patchy ground-glass opacities, often with consolidation of the dependent lung (9496). The later, organizing stage of AIP is associated with distortion of bronchovascular bundles and traction bronchiectasis. HRCT scoring of extent of abnormality is independently associated with mortality (93, 97). Biopsy shows an acute and/or organizing form of diffuse alveolar damage (DAD) that is indistinguishable from the histologic pattern found in ARDS (1). In the organizing phase, when most patients undergo biopsy, hyaline membranes may be inconspicuous or absent and the key findings include diffuse distribution, loose organizing connective tissue causing alveolar wall thickening and prominent pneumocyte hyperplasia. Occult background fibrosis may be present and if this shows features of UIP, acute exacerbation of underlying IPF should be considered (98). AIP can progress to a pattern similar to fibrotic NSIP (64) or to severe fibrosis resembling honeycombing (99).

Acute exacerbation of IIP.

Acute exacerbation occurs mostly in IPF, but is also found in other fibrosing interstitial pneumonias (100106). Diagnostic criteria have been published for acute exacerbation of IPF (107). In acute exacerbations of IPF, HRCT shows new bilateral ground-glass opacities and/or consolidation superimposed on a reticular pattern or honeycombing (Figures 6A and 6B) (108110). The pathology most often shows a mixed pattern of UIP and DAD (Figures 6C and 6D), but OP and prominent fibroblastic foci are also described as the acute component (103). It is important to exclude infection, left heart failure, and other identifiable causes of acute lung injury before diagnosing an acute exacerbation of an underlying IIP (107).

The category of rare IIPs has been created to include idiopathic lymphoid interstitial pneumonia (LIP) and idiopathic pleuroparenchymal fibroelastosis (PPFE). In addition, several rare histologic patterns of ILD have been described including AFOP and a group of bronchiolocentric patterns, although current data do not support these as distinct IIPs.

Idiopathic Lymphoid Interstitial Pneumonia

Most cases of LIP are associated with other conditions, although idiopathic cases still rarely occur (111). Idiopathic LIP has therefore been moved to the category of rare IIPs. The clinical, imaging, and histopathologic criteria for LIP proposed in 2002 remain unchanged, apart from recognition that some cases show striking cyst formation on HRCT (111, 112). Both the 2002 IIP classification and the ATS NSIP project demonstrated that many of the cases previously diagnosed as LIP are now considered cellular NSIP (1, 2). Consequently, few cases of idiopathic LIP have been published since 2002 (111).

Idiopathic Pleuroparenchymal Fibroelastosis

PPFE is a rare condition that consists of fibrosis involving the pleura and subpleural lung parenchyma, predominantly in the upper lobes. HRCT shows dense subpleural consolidation with traction bronchiectasis, architectural distortion, and upper lobe volume loss (Figures 7A and 7B) (113). The fibrosis is elastotic, and intraalveolar fibrosis is present (Figures 8A and 8B) (113117). It presents in adults with a median age of 57 years and has no sex predilection (113). Approximately half of patients have experienced recurrent infections. Pneumothorax is common. A minority has familial interstitial lung disease and nonspecific autoantibodies. Histologically, biopsies may show mild changes of PPFE or other patterns such as UIP. Disease progression occurs in 60% of patients with death from disease in 40% (113, 118).

Rare histologic interstitial pneumonia patterns have been described and these were not included as new IIP entities because of questions concerning whether they are variants of existing IIPs or exist only in association with other conditions such as HP or CVD. When encountered histologically, these terms may be of value in provisionally classifying biopsy features before MDD.

Acute Fibrinous and Organizing Pneumonia

AFOP was first reported in 17 patients with acute respiratory failure and initially regarded to represent a possible new IIP (119). The principal HRCT findings are bilateral basal opacities and areas of consolidation (Figure 9A). The dominant histologic pattern is intraalveolar fibrin deposition and associated organizing pneumonia (Figures 9C and 9D). Classical hyaline membranes of DAD are absent. AFOP may represent a histologic pattern that can occur in the clinical spectrum of DAD and OP or it may reflect a tissue sampling issue. AFOP may be idiopathic or associated with CVD (120), hypersensitivity pneumonitis (121), or drug reaction (122). As this pattern can be seen in eosinophilic pneumonia, this diagnosis should be excluded by absence of tissue and peripheral eosinophilia.

Bronchiolocentric Patterns of Interstitial Pneumonia

Several small retrospective series have recently described bronchiolocentric fibroinflammatory changes (123126). Of these, two studies in particular suggest these cases may be an IIP centered on airways (123, 125), although imaging findings were not well characterized and in one series there were environmental or occupational exposures in most cases (123). One study described cases of peribronchiolar metaplasia-ILD, which probably represent a form of small airway disease. The HRCTs in these cases were either normal or showed air trapping (124).

The 2002 ATS/ERS classification proposed an “unclassifiable” category of IIP, acknowledging that a final diagnosis may not be achieved, even after lengthy MDD (1). Examples of circumstances in which a case cannot be satisfactorily classified are summarized in Table 1 (127). Cases that are “unclassifiable” in terms of overlap of histologic patterns often prove to be related to CVD (e.g., interstitial pneumonia and follicular bronchiolitis in a patient with rheumatoid arthritis) or drug induced, rather than being idiopathic on MDD. If ILD is difficult, or impossible, to classify, management should be based on the most probable diagnosis after MDD and consideration of the expected disease behavior (as described below).

Patterns of disease behavior in diffuse lung disorders and related treatment approaches can be broadly subdivided as shown in Table 3. This approach is most useful in unclassifiable cases and for some IIPs, such as NSIP, that can be associated with all five patterns of disease behavior. This disease behavior classification is complementary to the IIP classification and should not be used as a justification for delaying SLB. Such delays increase the risk of surgical complications and may result in inappropriate management. This classification system needs to be validated for practicality and clinical relevance (127).


Clinical BehaviorTreatment GoalMonitoring Strategy
Reversible and self-limited (e.g., many cases of RB-ILD)Remove possible causeShort-term (3- to 6-mo) observation to confirm disease regression
Reversible disease with risk of progression (e.g., cellular NSIP and some fibrotic NSIP, DIP, COP)Initially achieve response and then rationalize longer term therapyShort-term observation to confirm treatment response. Long-term observation to ensure that gains are preserved
Stable with residual disease (e.g., some fibrotic NSIP)Maintain statusLong-term observation to assess disease course
Progressive, irreversible disease with potential for stabilization (e.g., some fibrotic NSIP)StabilizeLong-term observation to assess disease course
Progressive, irreversible disease despite therapy (e.g., IPF, some fibrotic NSIP)Slow progressionLong-term observation to assess disease course and need for transplant or effective palliation

Definition of abbreviations: COP = cryptogenic organizing pneumonia; DIP = desquamative interstitial pneumonia; HRCT = high-resolution computed tomography; IPF = idiopathic pulmonary fibrosis; NSIP = nonspecific interstitial pneumonia; RB-ILD = respiratory bronchiolitis–interstitial pneumonia.

*The distinctions in Table 3 are made by assimilating several factors: (1) A confident multidisciplinary diagnosis that often identifies the expected pattern of disease behavior (e.g., IPF). However, in other idiopathic interstitial pneumonias (e.g., NSIP) more than one pattern of behavior is possible; (2) disease severity, based on lung function and/or HRCT. In severe NSIP (154) a progressive irreversible course is frequent; (3) evaluation of potentially reversible and irreversible features based on review of the HRCT and biopsy if available; and (4) short-term disease behavior. Disease behavior classification must be refined over time in individual patients considering longitudinal changes in disease severity.

Identification of biomarkers has been focused on IPF and usually in small cohorts and without independent validation. However, some interesting findings have emerged that may have implications for diagnosis, management, or prognostication of other IIPs (Table 4). For example, rapidly declining lung function and/or reduced survival have been associated with high serum levels of some epithelial or macrophage-related proteins such as SP-A, SP-D, KL-6 (Krebs von den Lungen-6), CCL18 (chemokine ligand-18), and MMP-7 (matrix metalloproteinase-7) (29, 128131). These associations require validation, but suggest that biomarkers may be clinically useful to identify patients at high risk of progression.


BiomarkerPatientsHR (95% CI)P ValueReference
SP-A52 IPF (survivors vs. nonsurvivors) 0.0125Takahashi et al. (155)
SP-A142 IPF1.730.031Greene et al. (156)
KL-6 (>1,000 U/ml)27 IPF12.56 (1.195–131.90)0.035Yokoyama et al. (157)
KL-6 (≥1,000 U/ml)152 IIP and 67 CVD2.95 (1.71–5.08)0.0001Satoh et al. (129)
SP-D (≥253)82 IPF 0.0013Takahashi et al. (158)
KL-6 (>1.014)0.0087
Oxidative stress levels21 IPFFVC r = –0.79<0.01Daniil et al. (159)
DlCO r = –0.75<0.01
MMP-774 IPFHigher decline of DlCO (r = –0.53) and FVC (r = –0.51)0.002Rosas et al. (160)
SP-A82 IPF3.27 (1.49–7.17)0.003Kinder et al. (128)
SP-D (>460 ng/ml)72 IPF3.22 (1.33– 7.81)0.01Barlo et al. (29)
CCL18 above 150 ng/ml72 IPF7.98 (2.49–25.51)0.0005Prasse et al. (131)
CD4+CD28null > 18% of total CD489 IPF13.0 (1.6–111.1)0.0004Gilani et al. (161)
MMP-7, ICAM-1, IL-8, VCAM-1, S100-A12241 IPF (140, derivation; 101, validation)In the derivation cohort, high concentration predicted poor survival, poor transplant-free survival and poor progression-free survival. In the validation cohort high concentrations of all five were predictive of poor transplant-free survival; MMP-7, ICAM-1, and IL-8 of overall survival; and ICAM-1 of poor progression-free survivalOverall survival derivation cohortRichards et al. (162)
MMP-7: 0.0021
ICAM-1: 0.0015
IL-8: 0.029
VCAM-1: 0.00030
S100-A12: 0.0013
BAL20 IPFHigher in rapid progressors0.028McKeown et al.* (163)
MMP-8, MMP-90.015
BAL39 IPFHigher in nonsurvivors<0.02Shinoda et al.* (164)
BAL20 IPFNegative correlation with PFT Richter et al.* (165)
EndostatinFVC (r = –0.604)0.006
TlCO (r = –0.612)0.005

Definition of abbreviations: BAL = bronchoalveolar lavage; CI = confidence interval; CCL = chemokine ligand; CVD = collagen vascular disease; DlCO = diffusing capacity or transfer factor of the lung for carbon monoxide; HR = hazard ratio; ICAM = intercellular adhesion molecule; IPF = idiopathic pulmonary fibrosis; KL-6 = Krebs von den Lungen-6; MMP = matrix metalloproteinase; NS = not significant; PFT = pulmonary function test; S100-A12 = protein encoded by S100-A12 gene; SP = surfactant protein; TlCO = carbon monoxide diffusion factor; VCAM = vascular cell adhesion protein.

Regarding biomarkers for differential diagnosis, serum SP-A and SP-D were found significantly higher in IPF compared with NSIP/COP or CVD-IP, respectively (132, 133). Likewise, higher levels of serum DNA seem to distinguish patients with IPF from non-IPF patients (134). Studies in lungs and bronchoalveolar lavage fluid indicate that NSIP is characterized by a helper T-cell type 1–like pattern whereas a helper T-cell type 2–like response with increased expression of chemokine receptor-7 (CCR7) and CCL7 is observed in IPF (135138). Last, gene expression profiling has given contradictory results. Whereas one study found that most NSIP lungs did not resemble IPF, another identified only minor gene expression differences between UIP and NSIP (139).

Many association studies have failed to identify genetic polymorphisms that may confer increased risk of developing IPF (140, 141), whereas those showing association have not been validated in independent cohorts (140152).

This official statement was prepared by an ad hoc subcommittee of the Assembly on Clinical Problems.

Members of the ATS/ERS Committee on Idiopathic Interstitial Pneumonias:

  • William D. Travis, M.D. (Chair)

  • Talmadge E. King, Jr., M.D. (Co-Chair)

  • Ulrich Costabel, M.D. (Co-Chair)

  • Athol U. Wells, M.D. (Co-Chair)

  • Writing Committee

  • William D. Travis, M.D.

  • Ulrich Costabel, M.D.

  • David M. Hansell, M.D., M.P.H.

  • Talmadge E. King, Jr., M.D.

  • David A. Lynch, M.B.B.Ch.

  • Andrew G. Nicholson, D.M.

  • Christopher J. Ryerson, M.D.

  • Jay H. Ryu, M.D.

  • Moisés Selman, M.D.

  • Athol U. Wells, M.D.

  • Pulmonary

  • Jay H. Ryu, M.D. (Subcommittee Chair)

  • Jurgen Behr, M.D.

  • Demosthenes Bouros, M.D., Ph.D.

  • Kevin K. Brown, M.D.

  • Harold R. Collard, M.D.

  • Carlos Robalo Cordeiro, M.D., Ph.D.

  • Vincent Cottin, M.D., Ph.D.

  • Marjolein Drent, M.D., Ph.D.

  • Jim Egan, M.D., M.B.B.Ch.B.A.O.

  • Kevin Flaherty, M.D., M.S.

  • Yoshikazu Inoue, M.D., Ph.D.

  • Dong Soon Kim, M.D.

  • Fernando J. Martinez, M.D., M.S.

  • Ganesh Raghu, M.D.

  • Luca Richeldi, M.D., Ph.D.

  • Dominique Valeyre, M.D.

  • Radiology

  • David M. Hansell, M.D. (Subcommittee Co-Chair)

  • David A. Lynch, M.B.B.Ch. (Subcommittee Co-Chair)

  • Takeshi Johkoh, M.D., Ph.D.

  • Nicola Sverzellati, M.D.

  • Pathology

  • Andrew G. Nicholson, D.M. (Subcommittee Chair)

  • Thomas V. Colby, M.D.

  • Masanori Kitaichi, M.D.

  • Jeffrey Myers, M.D.

  • Molecular Biology

  • Moisés Selman, M.D. (Subcommittee Chair)

  • Bruno Crestani, M.D., Ph.D.

  • Cory Hogaboam, Ph.D.

  • James Loyd, M.D.

  • Evidence-based Analysis

  • Christopher J. Ryerson, M.D. (Subcommittee Chair)

  • Jeffrey Swigris, D.O., M.S.

  • Reference Librarians

  • Rosalind F. Dudden, M.L.S.

  • Shandra Protzko, M.S.

The committee acknowledges the American Thoracic Society and European Respiratory Society for supporting this project; the staff of the University of Modena and Reggio Emilia, Italy; Shandra Protzko and Rosalin Dudden of the Library and Knowledge Services, National Jewish Health, Denver, Colorado; the Department of Pathology, VU University Medical Center Amsterdam, Amsterdam, The Netherlands, and the Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York, New York for assistance with face-to-face meetings; the ATS staff for administrative assistance; and members of the ATS Documentation and Implementation Committee. The committee also acknowledges the following individuals who helped review the document: Arata Azuma (Japan), Mary Beth Beasley (United States), Alain Borczuk (United States), Marco Chilosi (Italy), Teri Franks (United States), Jeffrey Galvin (United States), Katrien Grunberg (The Netherlands), Richard Helmers (United States), Kevin Leslie (United States), Robert Kaner (United States), Heber MacMahon (United States), Nestor Muller (Brazil), David Naidich (United States), Marieke Overbeek (The Netherlands), Lynette Sholl (United States), Zarir F. Udwadia (India), and Dean W. Wallace (United States).

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This Official statement of the American Thoracic Society (ATS) and the European Respiratory Society (ERS) was approved by the ATS Board of Directors, June 2013, and by the ERS Steering Committee, March 2013

This document has an online supplement, which is accessible from this issue’s table of contents at

Author Disclosures: D.M.H. reported consulting for Astra Zeneca ($1,000–$4,999). T.E.K. reported serving on advisory committees of Immune Works ($1–4,999) and Intermune ($50,000–99,999). D.A.L. reported consulting for Gilead (no payments), Intermune (no payments), and Perceptive Imaging ($25,000–49,999); he received research support from Centocor ($25,000–49,999) and Siemens ($250,000+). A.G.N. reported consulting for Actelion ($50,000–99,999) and Boehringer Ingelheim ($10,000–49,999). C.J.R. reported serving as a speaker and on advisory committees of Intermune ($5,000–24,999), and received research support from Intermune ($50,000–99,999). J.B. reported serving as a consultant, speaker, and on advisory committees of Actelion ($25,000–49,999), and received research support from Actelion ($25,000–49,999); he served as a consultant, speaker, and on advisory committees of Boehringer Ingelheim ($5,000–24,999) and Intermune ($50,000–99,999); he received research support from Intermune ($25,000–49,999). K.K.B. served as a consultant for Almirall ($1–4,999), Amgen ($1–4,999), Array BioPharma ($1–4,999), Genzyme (no payments), GlaxoSmithKline (no payments), Ikaria ($1–4,999), Ironwood ($1–4,999), and Pfizer (no payments); he served on advisory committees of Actelion ($5,000–24,999), Array BioPharma ($1–4,999), Boehringer Ingelheim ($5,000–24,999), Centocor ($1–4,999), Fibrogen ($1–4,999), Genentech ($1–4,999), GeNo (no payments), Gilead ($5,000–24,999), Medimmune ($1–4,999), Mesoblast ($1–4,999), Promedior ($1–4,999), and Stromedix/Biogen ($1–4,999); he received research support from Actelion ($100,000–249,999), Amgen ($25,000–49,999), Genentech ($25,000–49,999), and Gilead ($5,000–24,999). H.R.C. reported consulting for Boehringer Ingelheim ($5,000–24,999), BMS ($1–4,999), Gilead ($5,000–24,999), and Promedior ($1–4,999); he served on advisory committees of Fibrogen ($5,000–24,999), Five Prime ($1–4,999), Genoa ($1–4,999), Medimmune ($1–4,999), and Mesoblast ($1–4,999), and received research support from Genentech ($5,000–24,999) and Intermune (no payments). V.C. reported serving as a speaker and on advisory committees of Intermune ($5,000–24,999); he served on advisory committees of Boehringer Ingelheim ($5,000–24,999) and received research support from Boehringer Ingelheim ($5,000–24,999). B.C. reported consulting for Sanofi ($1–4,999) and serving on advisory committees of Astra Zeneca ($1,000–4,999) and Intermune ($1–4,999); he was a speaker for Intermune ($1–4,999) and Stallergenes ($1–4,999), and received research support from Intermune ($100,000+). J.E. served on advisory committees of Pfizer (Wyeth) ($1–4,999). K.F. served as a speaker for GlaxoSmithKline ($10,000–49,999) and on advisory committees of Boehringer Ingelheim ($1–9,999), Fibrogen ($1–9,999), and GlaxoSmithKline ($1–9,999); he received research support from Centocor ($50,000–99,999), Immune Works ($50,000–99,999), and Intermune ($100,000+). D.S.K. served on advisory committees of Boehringer Ingelheim ($5,000–24,999). M.K. was patent holder with Daikin Industries of a process for preparing a fluorine-containing polymer and a cross-linked fluororubber diaphragm. F.J.M. reported consulting for Almirall ($1–4,999), American Institute for Research ($1–4,999), Astra Zeneca ($1–4,999), Bayer ($1–4,999), Boehringer Ingelheim ($5,000–24,999), Caden Jennings ($1–4,999), Cardiomema (no payments), Forest ($25,000–49,999), GlaxoSmithKline ($25,000–49,999), HCRC-TC ($1–4,999), Ikarta ($5,000–24,999), Medimmune ($1–4,999), Merck ($5,000–24,999), Merion-TC ($1–4,999), Novartis ($5,000–24,999), Pearl ($5,000–24,999), Pfizer ($1–4,999), Sudler-Hennessey-TC ($1–4,999), and Vertex ($1–4,999); he served as a speaker for Astra Zeneca ($1–4,999), Bayer ($5,000–24,999), Forest ($5,000–24,999), GlaxoSmithKline ($50,000–49,999), and Nycomed/Takeda ($50,000–49,999), and on advisory committees of Actelion ($5,000–24,999), Bayer ($1–4,999), Biogen/Stromedix ($1–4,999), Janssen ($1–4,999), Mpex (no payments), Nycomed/Takeda ($50,000–99,999), Pfizer ($1–4,999), and Vertex ($1–4,999); he received research support from Actelion ($5,000–24,999) and royalties from Informa ($1–4,999). G.R. reported consulting for Actelion ($5,000–24,999), Bayer ($1,000–4,999), Boehringer Ingelheim ($1–4,999), Centocor ($1–4,999), Celgene ($1–4,999), Fibrogen ($1–4,999), GlaxoSmithKline ($1–4,999), GeNo ($1–4,999), Gilead ($1–4,999), Intermune ($1–4,999), Promedior ($1–4,999), Sanofi-Aventis ($1–4,999), Stromedix ($1–4,999), and Takeda ($1–4,999). L.R. reported consulting for Fibrogen ($1–4,999) and Genentech ($1–4,999), and was a speaker for Boehringer Ingelheim ($1–4,999) and Intermune ($5,000–24,999); he served on advisory committees of Boehringer Ingelheim ($1–4,999), Intermune ($1–4,999), GlaxoSmithKline ($1–4,999), Medimmune ($1–4,999), and Sanofi-Aventis ($1–4,999); he received research support from Intermune ($50,000–99,999). J.S. consulted for Genentech ($1–4,999) and received research support from Intermune ($50,000–99,999). D.V. served on advisory committees of Actelion ($1–4,999) and as an expert witness for Sanofi-Aventis (<$1,000). W.D.T., U.C., J.H.R., M.S., A.U.W., D.B., T.V.C., C.R.C., M.D., R.F.D., C.H., Y.I., T.J., J.L., J.M., S.P., and N.S. reported they had no relevant commercial interests.


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