Interstitial lung diseases

Last updated: November 29, 2021

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Interstitial lung diseases (ILDs) are a heterogeneous group of disorders characterized by inflammation and progressive scarring (fibrosis) of the lungs. ILDs can be idiopathic (i.e., idiopathic interstitial pneumonias) or secondary to known causes such as autoimmune disease, changes in response to medical treatment, and diseases caused by exposure to radiation and inhalation of harmful substances. ILDs can lead to irreversible fibrosis and impaired pulmonary function. Cough and progressive exertional dyspnea are the most common symptoms. Bibasilar inspiratory crackles or rales are usually heard on auscultation. The treatment involves immune modulators, corticosteroids, and, in idiopathic pulmonary fibrosis, antifibrotic therapy (e.g., pirfenidone, nintedanib). Advanced stages of ILD can result in pulmonary insufficiency and respiratory heart failure with right ventricular insufficiency.

Idiopathic interstitial pneumonias (IIPs)

Secondary to a known cause

Exposure-related (environmental and occupational)

Secondary to underlying disease

Idiopathic pulmonary fibrosis (IPF)

Acute interstitial pneumonia (AIP)

  • Definition: a severe, acute ILD that can rapidly progress to respiratory failure
  • Epidemiology: most commonly affects individuals without preexisting lung conditions
  • Diagnostics: histologically characterized by diffuse alveolar damage

Cryptogenic organizing pneumonia (COP)

Nonspecific interstitial pneumonia (NSIP)

Desquamative interstitial pneumonia (DIP)

  • Definition: a rare type of ILD characterized by lung inflammation due to intraalveolar mononuclear infiltration
  • Epidemiology: affects men 40–50 years of age with a history of smoking
  • Diagnostics
    • Imaging studies show ground-glass opacities in the lower pulmonary lobes, usually without peripheral reticular opacities
    • Histologically characterized by intraalveolar accumulation of macrophages and thickening of alveolar septa

Respiratory bronchiolitis-interstitial lung disease (RBILD)

Lymphocytic interstitial pneumonia (LIP)

  • Definition: a rare ILD characterized by lymphocytic infiltration of the alveolar and alveolar septa
  • Epidemiology: affects adults (especially women) of all ages
  • Etiology: Associated with autoimmune (e.g., Sjögren disease, SLE) disorders, lymphoproliferative disorders, and HIV infection
  • Diagnostics: histologically characterized by diffuse alveolar and interstitial infiltration with plasma cells and polyclonal lymphocytes

Idiopathic pleuroparenchymal fibroelastosis (IPPFE)

  • Definition: a rare ILD characterized by pleural and subpleural fibrosis
  • Epidemiology: affects nonsmoker individuals between 50 and 60 years of age
  • Diagnostics
    • Imaging studies show pleural and subpleural thickening of the upper pulmonary lobes on imaging studies
    • Histological findings include intraalveolar fibrosis and elastosis of the alveolar walls


Advanced disease

Due to the wide variety of subtypes and symptoms, there is no universal diagnostic algorithm. Complete medical history, physical examination, serology, imaging (chest X-ray, CT scan), and pulmonary function tests should be performed in all patients with symptoms of ILD. Lavage and biopsy can help identify confounding conditions (e.g., infection, malignancy) and confirm the diagnosis of a given type or stage of ILD. [7]

Complete medical history

Laboratory tests


Chest X-ray

  • Normal in approx. 10% of patients
  • Increase in reticular opacities (sign of fibrosis)
  • Patients may have nodular or mixed patterns
  • Ground-glass opacities


Pulmonary function tests (spirometry, lung volumes, diffusing capacity)

Bronchoalveolar lavage [8]

Surgical biopsy

  • Indications
    • Inconclusive initial evaluation
    • Atypical or rapidly progressive symptoms
    • Disease exacerbation
    • Ambiguous pulmonary function tests
  • In patients with minimal signs or symptoms and stable disease: close observation (e.g., PFTs, HRCTs over several months) may be sufficient.

Additional tests


Differential diagnoses of pneumoconioses [11][12]
Type Etiology Population at risk Clinical features Chest x-ray
  • Asbestos miners and millers
  • Brake linings and insulation manufactures
  • Ship construction workers
  • Demolishers
  • Firefighters
  • Plumbers
  • Roofers
  • Diffuse bilateral infiltrates predominantly in the lower lobes
  • Interstitial fibrosis
  • Calcified pleural plaques (usually indicate benign pleural disease)
  • Supradiaphragmatic and pleural reticulonodular opacities/plaques
  • Crystalline silica dust
  • Miners
  • Workers of quarries, pottery production, sandblasting, glass manufacturers
  • Construction workers
  • Eggshell calcifications
  • Large number of rounded, solitary, small (< 1 cm) opacities particularly in the upper lobe of the lungs
  • Bilateral diffuse ground-glass opacities
Aluminosis [13][14]
  • Aluminum dust
  • Welders (e.g., automobile industry)
  • Nodular or diffuse infiltrates (predominantly affect the upper lung fields)
  • Small cystic radiolucencies (honeycombing) [14]
Anthracosis [15][16]
  • Carbon dust and sooty air
  • Urban population
  • Coal miners
  • Heterogeneous pulmonary infiltrates, with/without mass lesion
Coal workers' pneumoconiosis [15][16]
  • Fine nodular opacifications (< 1 cm) in upper lung zone
  • Beryllium
  • Workers in manufacturing industries where alloys are frequently used (often high-tech)
    • Aerospace engineering
    • Ceramics industries
    • Dental material production
    • Nuclear and electronics plants
    • Dye manufacturing
    • Foundries
Pulmonary siderosis [19][20]
  • Welders, iron miners, foundry workers
  • Usually asymptomatic
  • Occasionally, presents with features similar to COPD
  • Complications: pulmonary fibrosis (rarely occurs)
  • Small, round, patchy shadows on x-ray
Organic dust toxic syndrome
  • Organic dust contaminated with mycotoxins (e.g., from moldy grain or hay)
  • Farmers working with grain, hay, silage, and confined animals (e.g., swine and poultry)
  • N/A
Byssinosis [21]
  • Mainly dust from raw cotton
  • Less commonly: flax, jute, hemp, and sisal dust
  • Textile industry workers
  • Symptoms diminish with prolonged exposure but manifest again with increased severity upon reexposure after a period nonexposure, e.g., a weekend.
  • Acute byssinosis
  • Chronic byssinosis
    • Disappearance of cyclical symptoms
    • Chronic productive cough
  • Complications: pulmonary fibrosis
  • Diffuse haziness, predominantly in the lower lobes of the lungs.

Although coal is mined from under the earth, the upper lobes of the lungs are primarily affected.

Treatment choices and prognosis for ILD vary depending on type and cause.

General measures

Further general measures not applicable to IPF

Idiopathic interstitial pneumonias

Idiopathic pulmonary fibrosis

Other idiopathic interstitial pneumonias

We list the most important complications. The selection is not exhaustive.

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