Interstitial lung diseasesJ84.9

Interstitial lung diseases (also known as parenchymal lung diseases) are a heterogeneous group of pulmonary diseases characterized by thickening of the alveolar septa, fibroblast proliferation, collagen deposition and, if the disease progresses unhindered, pulmonary fibrosis. Interstitial lung diseases can be classified according to various criteria (e.g. acute versus chronic, granulomatous versus non-granulomatous, known cause versus unknown cause, primary lung disease versus secondary consequence of systemic disease, history of smoking versus history of non-smoking).

A) Known causes (50 % of cases):

• Infections (e.g. Pneumocystis jirovecii, viruses, see also ARDS)
• Inhalative noxae
  • Inorganic dusts: pneumoconiosis(silicosis, asbestosis, berylliosis, etc.)
  • Organic dusts: Exogenous allergic alveolitis (EAA)
  • Smoking (Smoking related ILD [SR-ILD])
  • Gases, vapors, aerosols of various hazardous substances, hairspray
• Non-inhaled noxious substances
  • Pharmaceuticals (e.g. bleomycin, busulfan, amiodarone)
  • Herbicides (e.g. paraquat)
  • Ionizing radiation(radiation pneumonitis)
• Systemic diseases:
  • Sarcoidosis (Boeck's disease)
  • Rheumatic diseases: rheumatoid arthritis, collagenoses (CTD-ILD), vasculitis, dermatomyositis, systemic scleroderma
  • Storage diseases: amyloidosis, Gaucher's disease, etc.
• Intestinal and liver diseases
  • Crohn's disease, ulcerative colitis
  • Primary biliary cirrhosis, chronic active hepatitis
• Diffuse alveolar haemorrhage (DAH/pulmonary haemorrhage syndromes), Goodpasture's syndrome, ANCA-associated vasculitis, idiopathic pulmonary siderosis, anticoagulant overdoses
• Congenital diseases
  • Tuberous sclerosis
  • Neurofibromatosis
  • Niemann-Pick disease
• Graft-versus-host reaction

B) Unknown causes

• Idiopathic interstitial pneumonia (IIP) Prevalence: approx. 70 (f) or 80 (m)/100,000. Classification of IIP (ATS = American Thoracic Society and ERS = European Respiratory Society, 2013) -
• 1. main forms of idiopathic interstitial pneumonia (major IIPs)
• Chronic fibrosing IIPs
• Idiopathic pulmonary fibrosis (IPF, 55%)
• Non-specific interstitial pneumonia (NSIP, 25%) 95%
• Tobacco smoke-associated IIPs (SR-ILD, 15%)
  • Respiratory bronchiolitis interstitial lung disease (RB-ILD)
  • Desquamative interstitial pneumonia (DIP)
  • Pulmonary Langerhans cell histiocytosis (PLCH)
• Acute/subacute IIPs
  • Cryptogenic organizing pneumonia (COP, 3%)
  • Acute interstitial pneumonia (AIP, 1%)
• 2.rare idiopathic interstitial pneumonia (rare IIPs)
  • Lymphocytic interstitial pneumonia (LIP, <1%)
  • Pleuroparenchymal fibroelastosis (PPFE)
• 3. unclassifiable idiopathic interstitial pneumonia (unclassifiable IIPs)

Incidence: 10 - 25/100 000/year.

The term "interstitial lung disease" covers more than 300 different diseases. Most of them are rare. The most common interstitial lung diseases include:

• Sarcoidosis
• Idiopathic pulmonary fibrosis
• Extrinsic allergic alveolitis (also known as hypersensitive pneumonitis)
• Interstitial lung diseases associated with tissue diseases
• Pneumoconiosis
• Interstitial lung diseases caused by certain drugs used to treat other diseases
• Some interstitial lung diseases, especially sarcoidosis, also affect other organs of the body.