An official American Thoracic Society/European Respiratory Society statement: Update of the international multidisciplinary classification of the idiopathic interstitial pneumonias

Abstract

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.

Figure 1.

Atypical usual interstitial pneumonia/idiopathic pulmonary fibrosis. Computed tomography (CT) features: (A) CT image of atypical usual interstitial pneumonia (UIP). Prone axial CT through the lung bases in a patient with histologically proven UIP shows predominantly peribronchovascular ground-glass/reticular opacities with traction bronchiectasis. Under the ATS/ERS/JRS/ALAT Statement (8), this would be classified as inconsistent with UIP. Histologic features: (B) The biopsy shows patchy subpleural dense fibrosis with honeycomb change adjacent to preserved lung. (C) Dense scarring fibrosis is present with a small nodular fibroblastic focus.

Figure 2.

Nonspecific interstitial pneumonia. Computed tomography (CT) features: (A) Axial and (B) coronal CT reconstructions show confluent bilateral lower lobe ground-glass opacities with marked traction bronchiectasis and lower lobe volume loss. The peribronchovascular predominance with subpleural sparing is well shown on the axial image. (C and D) Histologic features: Lung biopsy shows diffuse alveolar wall thickening by uniform fibrosis. The alveolar architecture is preserved and no honeycombing or fibroblastic foci are seen. Interstitial inflammation is mild.

Figure 3.

Respiratory bronchiolitis–interstitial lung disease. (A) Axial and (B) coronal computed tomography (CT) reconstructions in a 47-year-old heavy cigarette smoker show moderately extensive ground-glass opacities and centrilobular nodules (circles). The bronchi are markedly thick-walled and there is minimal emphysema. Bronchoalveolar lavage yielded 91% macrophages. (C) Histologic features: lung biopsy shows peribronchiolar pigmented macrophage accumulation and emphysema. (D) There is mild bronchiolar fibrosis and pigmented macrophages within airspaces.

Figure 4.

Cryptogenic organizing pneumonia. Computed tomography (CT) features with (A) peripheral consolidation and air bronchograms, (B) bronchocentric distribution, (C) perilobular pattern showing focal right lower lobe consolidation, with more central ground-glass opacity, corresponding to the reversed halo sign, and (D) bandlike consolidation.

Figure 5.

Fibrotic hypersensitivity pneumonitis. (A) Axial and (B) coronal computed tomography (CT) reconstructions in a 76-year-old bird-keeper with progressive shortness of breath over 6 years show upper lung–predominant subpleural reticulation with some confluent areas of dense opacification, traction bronchiectasis, and patchy ground-glass opacities. Honeycombing is not identified. (C) Histology shows a bronchiolocentric cellular and fibrosing interstitial pneumonia. (D) There is a patchy cellular interstitial infiltrate and poorly formed granulomas.

Figure 6.

Acute exacerbation of idiopathic pulmonary fibrosis (IPF). Computed tomography (CT) features: (A) Axial image through the upper lungs at baseline shows mild peripheral, basal predominant reticular abnormality without honeycombing and mild emphysema. (B) Axial image during an acute exacerbation 4 months later shows extensive new bilateral ground-glass opacities, with some superimposed reticular abnormality. (C and D) Histologic features: (C) Usual interstitial pneumonia pattern with honeycomb fibrosis and fibroblastic foci. (D) Focally, features of diffuse alveolar damage are present with uniform thickening of alveolar walls and hyaline membranes.

Figure 7.

Pleuroparenchymal fibroelastosis. Computed tomography (CT) features: (A) High-resolution computed tomography (HRCT) through the upper lobes shows irregular pleural-based opacities and a reticular pattern associated with parenchymal distortion. The pleura and lungs in the lower lobes appeared normal. (B) Section through the upper lobes shows scattered pleuroparenchymal opacities and some distortion of the underlying lung parenchyma. In the lower lobes there was no pleural irregularity, but there was a subtle subpleural reticular pattern.

Figure 8.

Pleuroparenchymal fibroelastosis. (A) Low power shows pleural thickening and subpleural fibrosis. (B) Dense masses of elastic fibers are highlighted beneath the fibrotically thickened pleura (elastic stain).

Figure 9.

Acute fibrinous and organizing pneumonia. Computed tomography (CT) features. (A) Axial CT through the lung bases shows multiple poorly defined nodules and areas of consolidation, with peribronchovascular and basal predominance. Pleural and pericardial effusions are present. Histologic features: (B) Biopsy shows nodules of alveolar fibrin and organizing pneumonia. (C) The histology is dominated by intraalveolar plugs of alveolar fibrin.