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ILD Classification - 2025 ERS/ATS Statement (Updated)
The most current authoritative document is the 2025 ERS/ATS Statement - "Update of the International Multidisciplinary Classification of the Interstitial Pneumonias" (Ryerson CJ et al., Eur Respir J, 2025; DOI: 10.1183/13993003.00158-2025, PMID: 40774805). This supersedes the 2013 ATS/ERS statement and introduces four major advances.
The 4 Major Advances in the 2025 Statement
1. Expanded Scope - Beyond Idiopathic IIPs
The new classification moves beyond purely idiopathic interstitial pneumonias (IIPs) to include secondary causes - CTD-ILD, hypersensitivity pneumonitis (HP), drug-induced ILD, and others - creating a truly unified ILD framework.
2. New Subcategories and Updated Terminology
| Old Term (2013) | New Term (2025) | Rationale |
|---|---|---|
| Acute Interstitial Pneumonia (AIP) | Idiopathic Diffuse Alveolar Damage (iDAD) | Aligns pattern name with underlying pathology |
| Desquamative Interstitial Pneumonia (DIP) | Alveolar Macrophage Pneumonia (AMP) | Better reflects macrophage-filling rather than desquamation |
| - | Bronchiolocentric Interstitial Pneumonia (BIP) | NEW major pattern covering airway-centered injury |
BIP is now an overarching term for airway-centered histologic/radiologic patterns seen in HP, CTD-ILD, aspiration, and drug-induced ILD. This allows UIP, NSIP, and BIP to serve as the three main fibrosing interstitial pneumonia patterns.
3. Subclassification into Interstitial and Alveolar Filling Disorders
The classification is reorganized by the predominant anatomical location of lung injury:
A. Interstitial Disorders
Further split by disease behavior:
Fibrotic Interstitial Disorders
- Usual Interstitial Pneumonia (UIP) - pattern of IPF and other fibrosing ILDs
- Nonspecific Interstitial Pneumonia (NSIP)
- Bronchiolocentric Interstitial Pneumonia (BIP) - new major fibrotic pattern
- Pleuroparenchymal Fibroelastosis (PPFE)
Non-Fibrotic Interstitial Disorders
- Cryptogenic Organizing Pneumonia (COP) / Organizing Pneumonia (OP)
- Lymphoid Interstitial Pneumonia (LIP)
- Idiopathic DAD (formerly AIP)
B. Alveolar Filling Disorders
Subgrouped by the type of cell/fluid filling the alveoli:
- Organizing Pneumonia (OP) - polypoid fibroblastic plugs in alveoli and alveolar ducts
- Respiratory Bronchiolitis-ILD (RB-ILD)
- Alveolar Macrophage Pneumonia (AMP) - formerly DIP
- Pulmonary Alveolar Proteinosis (PAP)
- Eosinophilic Pneumonias
- Alveolar Hemorrhage Syndromes
4. Diagnostic Confidence Tiers
The 2025 statement formalizes diagnostic confidence at both radiologic and histologic levels:
| Confidence Level | Probability |
|---|---|
| Confident diagnosis | ≥90% |
| Provisional diagnosis | 51-89% |
| Unclassifiable ILD | <50% or no leading diagnosis |
This applies to HRCT patterns and biopsy findings alike, acknowledging that as many as 12% of ILD cases remain unclassifiable.
Broader ILD Classification (Clinical Categories)
From Goldman-Cecil Medicine (Table 80-1) and the 2025 ERS/ATS framework, the full clinical ILD classification includes:
1. Idiopathic Interstitial Pneumonias (IIPs)
Reorganized in 2025 under fibrotic vs. non-fibrotic
- Major fibrosing: IPF (UIP pattern), iNSIP, BIP-associated IIP
- Non-fibrosing/acute: COP, iDAD (formerly AIP), LIP
- Smoking-related: RB-ILD, AMP (formerly DIP)
- Rare: PPFE, AFOP (Acute Fibrinous and Organizing Pneumonia)
2. ILD Associated with Connective Tissue Disease (CTD-ILD)
- Systemic sclerosis (most common CTD-ILD; NSIP pattern predominant)
- Rheumatoid arthritis (UIP or NSIP)
- Polymyositis/Dermatomyositis
- Systemic lupus erythematosus
- Sjogren syndrome
- Mixed connective tissue disease
- Ankylosing spondylitis
3. Hypersensitivity Pneumonitis (HP)
- Occupational/environmental (farmer's lung, bird fancier's lung)
- Iatrogenic
- BIP pattern is now the preferred histologic descriptor for HP on biopsy
4. Drug-Induced and Iatrogenic ILD
- Amiodarone, methotrexate, checkpoint inhibitors, chemotherapy agents, nitrofurantoin (see dedicated drug tables)
5. Granulomatous ILD
- Sarcoidosis
- Langerhans Cell Histiocytosis (LCH)
- Hypersensitivity pneumonitis (granulomatous subtype)
6. ILD Associated with Pulmonary Vasculitis
- Granulomatosis with Polyangiitis (GPA, formerly Wegener's)
- Microscopic Polyangiitis
- Eosinophilic Granulomatosis with Polyangiitis (Churg-Strauss)
7. Other Specific Forms
- Lymphangioleiomyomatosis (LAM)
- Pulmonary capillaritis
- Combined Pulmonary Fibrosis and Emphysema (CPFE) - recognized by 2022 ATS/ERS/JRS/ALAT Research Statement (PMID: 35969190)
Progressive Pulmonary Fibrosis (PPF) - 2022 ATS/ERS/JRS/ALAT Addition
The 2022 ATS/ERS/JRS/ALAT guideline (PMID: 35486072) introduced Progressive Pulmonary Fibrosis (PPF) as a functional/behavioral designation (not a standalone diagnosis) - applied when non-IPF ILDs (HP, CTD-ILD, iNSIP, etc.) demonstrate progressive worsening despite treatment, warranting antifibrotic therapy.
Key Takeaways
- The 2025 ERS/ATS statement is the most current ILD classification update, replacing the 2013 document
- The biggest structural change is the fibrotic vs. non-fibrotic interstitial / alveolar filling subclassification
- BIP is a brand-new major pattern covering HP, CTD-ILD, aspiration, and drug-induced ILD with airway-centered injury
- iDAD and AMP are the new preferred terms for what was AIP and DIP respectively
- Diagnostic confidence tiers are now applied consistently at both HRCT and histologic levels
Goldman-Cecil Medicine, Table 80-1 (clinical classification); Ryerson CJ et al., Eur Respir J 2025, PMID 40774805 (2025 ERS/ATS Statement); Raghu G et al., Am J Respir Crit Care Med 2022, PMID 35486072 (2022 IPF/PPF guideline)
Just tell me classification not ur drama and from only ats and ers
2025 ERS/ATS Classification of Interstitial Pneumonias
INTERSTITIAL DISORDERS
Fibrotic
- UIP (Usual Interstitial Pneumonia)
- NSIP (Nonspecific Interstitial Pneumonia)
- BIP (Bronchiolocentric Interstitial Pneumonia) ← new major pattern
- PPFE (Pleuroparenchymal Fibroelastosis)
Non-Fibrotic
- OP (Organizing Pneumonia) / COP
- LIP (Lymphoid Interstitial Pneumonia)
- iDAD (Idiopathic Diffuse Alveolar Damage) ← replaces AIP
ALVEOLAR FILLING DISORDERS
- OP / COP
- RB-ILD (Respiratory Bronchiolitis-ILD)
- AMP (Alveolar Macrophage Pneumonia) ← replaces DIP
- AFOP (Acute Fibrinous and Organizing Pneumonia)
BY ETIOLOGY
| Category | Examples |
|---|---|
| Idiopathic (IIPs) | IPF, iNSIP, COP, iDAD, RB-ILD, AMP, LIP, PPFE |
| CTD-ILD | SSc, RA, PM/DM, SLE, Sjögren, MCTD |
| Hypersensitivity Pneumonitis | Environmental, occupational, drug |
| Drug-induced ILD | Amiodarone, MTX, checkpoint inhibitors |
| Granulomatous | Sarcoidosis, LCH |
| Unclassifiable ILD | ~12% of cases |
Diagnostic Confidence (applied at HRCT + histology):
- Confident ≥90% | Provisional 51-89% | Unclassifiable <50%
Source: Ryerson CJ et al., ERS/ATS Statement, Eur Respir J 2025 — PMID 40774805
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