Lung
Other nonneoplastic conditions
Acute lung injury
Acute interstitial pneumonia
Last author update: 1 October 2017
Last staff update: 8 September 2023
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PubMed search: Acute interstitial pneumonia [title]
Table of Contents
Definition / general | Essential features | Terminology | ICD coding | Epidemiology | Sites | Pathophysiology | Etiology | Clinical features | Diagnosis | Laboratory | Radiology description | Radiology images | Prognostic factors | Case reports | Treatment | Gross description | Gross images | Microscopic (histologic) description | Microscopic (histologic) images | Cytology description | Cytology images | Positive stains | Electron microscopy description | Differential diagnosis | Additional references | Board review style question #1 | Board review style answer #1Cite this page: Yoshikawa A, Fukuoka J. Acute interstitial pneumonia. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/lungnontumoracuteinterstitialp.html. Accessed April 26th, 2024.
Definition / general
- In 1935, Hamman and Rich first reported autopsy cases of initially healthy individuals who developed a rapidly progressive and fatal type of interstitial lung disease, which differed from other interstitial pneumonia clinically and pathologically (Trans Am Clin Climatol Assoc 1935;51:154)
- Katzenstein et al. coined the term "acute interstitial pneumonia (AIP)" (Am J Surg Pathol 1986;10:256)
- In the multidisciplinary classification of idiopathic interstitial pneumonias by American Thoracic Society / European Respiratory Society, acute interstitial pneumonia is categorized as "acute / subacute interstitial pneumonia" (Am J Respir Crit Care Med 2013;188:733)
Essential features
- Rare and aggressive type of idiopathic interstitial pneumonia with diffuse alveolar damage (DAD), characterized by diffuse inflammation with hyaline membrane and fibroblastic proliferation
- Acute interstitial pneumonia shares common features with acute respiratory distress syndrome (ARDS) clinically and morphologically
Terminology
- Also called Hamman-Rich syndrome and idiopathic diffuse alveolar damage
ICD coding
Epidemiology
- Extremely rare (no conclusive epidemiological data available)
- Mean age 50 years but can occur at any age (7 - 83 years) (Eur Respir J 2000;15:412)
- No sex predilection
Sites
- Bilateral lung, usually in all five lobes of the lung
Pathophysiology
- Both endothelial and epithelial injury result in decreased integrity of the alveolar capillary membrane
- Imbalance of proinflammatory and anti-inflammatory mediators
- Neutrophils increase in alveoli and interstitium and release metabolites leading to lung injury
- Alveolar epithelial cells may go through epithelial - mesenchymal transition to become myofibroblasts, resulting in interstitial organization and fibrosis (BMC Pulm Med 2014;14:67)
Etiology
- No definite cause; no risk factors have been identified
Clinical features
- Influenza-like illness, followed by progressive shortness of breath (Am J Surg Pathol 1986;10:256)
- Vast majority of patients are previously healthy and lack history of lung disease
- Many clinical characteristics of acute interstitial pneumonia are similar to acute respiratory distress syndrome (Chest 2003;124:554)
- Acute interstitial pneumonia can progress to respiratory failure as profound as severe acute respiratory distress syndrome (PaO2/FIO2 ≤ 100 mm Hg) and almost all patients need mechanical ventilation and hospital care
- Respiratory failure usually appears 1 - 3 weeks from the onset, later than acute respiratory distress syndrome (16.8 days vs. 2.2 days)
- Multiple organ failure is less common in acute interstitial pneumonia
Diagnosis
- Diagnostic requirements
- Exclusion of any other causes of respiratory failure
- Histological diagnosis of diffuse alveolar damage
- Open lung biopsy, if possible, is recommended to reach the accurate diagnosis and to guide prompt treatment (Crit Care 2006;10:423)
- Transbronchial lung biopsy may be also helpful to find hyaline membranes of diffuse alveolar damage but it needs to be carefully distinguished from artifacts
Laboratory
- Hypoxia
- Increased serum ferritin, D dimer and C reactive protein
- KL-6 may increase slightly
Radiology description
- Heterogeneous bilateral ground glass opacity due to pulmonary edema
- Chest radiograph
- Ground glass opacity
- Consolidation with air bronchogram
- Chest CT
- Ground glass opacity
- Airspace consolidation
- Bronchiolectasis / bronchiectasis; related to worse prognosis (Am J Respir Crit Care Med 2002;165:1551)
- Volume reduction
Radiology images
Images hosted on other servers:
Chest radiograph
Exudative phase on CT
Organizing phase on CT
Comparison on CT and histology
Prognostic factors
- Most patients die within 2 months unless appropriate treatment is provided (Eur Respir J 2000;15:412)
- High dose steroid therapy drastically improves the prognosis with long term survival of more than 80% (Chest 2006;129:753, Chest 2003;124:554)
- Survivors may suffer recurrences or develop chronic lung injury
Case reports
- 3 year old girl died of acute interstitial pneumonia (J Korean Med Sci 2008;23:529)
- 51 year old woman died of acute interstitial pneumonia (Case Rep Pulmonol 2012;2012:678249)
Treatment
- Oxygen therapy for respiratory failure
- Mechanical ventilation with positive end expiratory pressure
- High dose steroid pulse (Chest 2006;129:753)
- Direct hemoperfusion using polymyxin B immobilized fiber column was recently found to effectively improve the prognosis of acute interstitial pneumonia patients (Ther Adv Respir Dis 2017;11:261)
Gross description
- Dark blue lungs with hemorrhagic dots on pleural surface
- Heavy and firm due to edema and fibrosis
- Dilatation of alveolar ducts
Gross images
Contributed by Yale Rosen, M.D.
Gross images of diffuse alveolar damage
Microscopic (histologic) description
- Acute interstitial pneumonia shows diffuse alveolar damage, which is almost completely identical to acute respiratory distress syndrome / diffuse alveolar damage morphologically (Eur Respir J 2000;15:412)
- Proliferative / organizing (subacute) phase of diffuse alveolar damage is most common in acute interstitial pneumonia but also exudative (acute) phase and fibrotic (chronic) phase can be seen
- Exudative phase
- Hyaline membranes in alveolar duct or sacs; scattered or not apparent, unlike in acute respiratory distress syndrome
- Interstitial and intra-alveolar edema
- Collapsed alveoli
- Denudation and necrosis of type I pneumocytes
- Hemorrhage, usually mild
- Proliferative / organizing phase (Am J Surg Pathol 1986;10:256, Eur Respir J 2003;21:187)
- Organizing pneumonia with / without remnants of hyaline membrane
- Interstitial and intra-alveolar proliferation of fibroblasts / myofibroblasts
- Lymphocytic infiltration; usually more prominent than in acute respiratory distress syndrome
- Proliferation of type II pneumocytes with occasional cellular atypia
- Endothelial injury and fibrinous thromboembolism in arterioles / arteries
- Fibrosis phase
- Diffuse collagenous fibrosis
- Microscopic honeycomb-like change
- Traction bronchiolectasis
- Squamous metaplasia
- Organized thrombus
- Thickening of pleura with dilatation of lymphatic / blood vessels
Microscopic (histologic) images
Contributed by Akira Yoshikawa, M.D. and Yale Rosen, M.D.
Low power
Architectural destruction
Fibroblastic proliferation
Type II pneumocyte hyperplasia
Lymphocytic infiltration
Epithelial denudation
Dense fibrosis with smooth muscle hyperplasia
Organizing phase - proliferation of fibroblasts and type II pneumocytes
Images hosted on other servers:
Organizing phase
Organizing phase - fibroblastic proliferation
Exudative phase and organizing phase
Cytology description
- Bronchoalveolar lavage (BAL) fluid
- Increased neutrophils (Eur Respir J 2000;15:412)
- Atypical epithelial cells are rarely present (Eur Respir J 2003;21:187)
Cytology images
Images hosted on other servers:
Atypical epithelial cells in BAL fluid
Positive stains
- Elastica van Gieson (fiber staining) is helpful to evaluate architectural destruction of alveoli
Electron microscopy description
- Proliferation of type II pneumocyte with cytoplasmic projection into alveolar septa, abnormally large lamellar bodies or denudation from basement membrane (Am J Surg Pathol 1986;10:256)
Differential diagnosis
- Acute exacerbation of interstitial lung disease, especially idiopathic pulmonary fibrosis (IPF): history of IPF, background of dense fibrosis and honeycombing
- Acute hypersensitivity pneumonitis: history of exposure to causative antigens, remission of symptoms after antigen removal, lymphocytosis ( > 30%) in bronchoalveolar lavage, nonnecrotizing granulomas, strong bronchocentric accentuation
- Acute respiratory distress syndrome: predisposition of pulmonary or systemic insult, an onset within 7 days, PaO2/FIO2 ≤ 300 mm Hg
- Collagen tissue disease associated interstitial lung disease
- Several collagen tissue disease are known to rarely present with acute interstitial pneumonia-like symptoms and diffuse alveolar damage (Mod Rheumatol 2012;22:243, Chest 2006;130:553)
- Clinical manifestation and serum autoantibody tests are helpful for the diagnosis
- Drug induced lung injury: history of causative drug, remission of symptoms after drug withdrawal, marked eosinophils, foamy changes in type II cells
- Eosinophilic pneumonia: smoking history, eosinophilia ( > 25%) in bronchoalveolar lavage, degranulation of eosinophils in the lung tissue, pink macrophages, marked gumball airspace fibrin rather than hyaline membranes
- Organizing pneumonia: exposure to causative particles, migratory shadows on radiology, preservation of alveolar architecture
Additional references
Board review style question #1
Which of the following findings is not required for the diagnosis of acute interstitial pneumonia?
- Absence of exposure to causative factors of respiratory failure
- Absence of prior history of lung disease
- Bilateral shadows on chest radiograph
- Diffuse alveolar damage on histology
- PaO2/FIO2 ≤ 300 mm Hg
Board review style answer #1
E. PaO2/FIO2 ≤ 300 mm Hg is one of the diagnostic criteria of acute respiratory distress syndrome. Acute interstitial pneumonia can also cause the similar severe respiratory failure, however it is not a diagnostic requirement for acute interstitial pneumonia.
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Reference: Acute interstitial pneumonia
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Reference: Acute interstitial pneumonia
