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Internal Medicine

Idiopathic interstitial pneumonia (IIP)

Chronic, progressive fibrosing interstitial pneumonia characterized by idiopathic origin, occurrence primarily in older adults, exclusively pulmonary involvement and pattern of Usual Interstitial Pneumonia (UIP) proven by histopathology and/or radiology

Chronic, progressive fibrosing interstitial pneumonia characterized by idiopathic origin, occurrence primarily in older adults, exclusively pulmonary involvement and pattern of Usual Interstitial Pneumonia (UIP) proven by histopathology and/or radiology

History:

Louis Hamman and Arnold Rich published a paper describing diffuse interstitial fibrosis of the lung in 1944. They described thickening of the alveolar interstitium and an area of dense fibrotic scar tissue within the lung. Liebow and Carrington heralded the modern era of interstitial lung disease histo-pathology with the notion that IIP could be split into separate pathological subtypes in 1969. In 2002, a panel of experts sponsored jointly by the American Thoracic Society (ATS) and the European Respiratory Society (ERS) released an official statement for the purpose of providing a new and comprehensive classification of IIP that considered all clinical, radiographic and pathological features.

Classification

Interstitial lung disease (ILD):

Interstitial lung disease (ILD), sometimes called diffused parenchymal diseases is a group of diseases characterized by a combination of chronic inflammation within the lung, consisting of an accumulation of chronic inflammatory cells (predominantly lymphocytes and macrophages) and increased levels of numerous pro-inflammatory cytokines, chemokines, and cell surface molecules; and varying degrees of lung fibrosis.

American Thoracic Society/European Respiratory Society (ATS/ERS) 2002 consensus classification statement:

Histopathologic classification separating the IIPs into seven clinicopathologic entities (in order of relative frequency)
  • Idiopathic pulmonary fibrosis (IPF) (47-64%)
  • Nonspecific interstitial pneumonia (NSIP) (14-36%)
  • Respiratory bronchiolitis ILD(10-17%)
  • Cryptogenic organizing pneumonia (4-12%)
  • Acute interstitial pneumonia (AIP) (< 2%)
  • Lymphoid interstitial pneumonia (LIP) (< 2%)

Aetiology

Schematic classification of interstitial lung diseases according to aetiology. The finding of histological usual interstitial pneumonitis in a patient with an idiopathic interstitial pneumonia leads to the specific diagnosis of idiopathic pulmonary fibrosis. | NSIP = non-specific interstitial pneumonitis. | Mikolasch, T. A., Garthwaite, H. S., & Porter, J. C. (2017). Update in diagnosis and management of interstitial lung disease . Clinical medicine (London, England), 17(2), 146–153. https://doi.org/10.7861/clinmedicine.17-2-146

Diagnosis

Diagnostic criteria for a definite usual interstitial pneumonitis pattern on high resolution computerised tomography: 1 – subpleural, basal predominance (red arrows); 2 – reticular abnormality (blue arrow); 3 – honeycombing with or without traction bronchiectasis (yellow arrow); 4 – absence of features inconsistent with usual interstitial pneumonitis pattern. | BAL = bronchoalveolar lavage; GOR = gastro-oesophageal reflux; HRCT = high-resolution computerised tomography; ILD = interstitial lung disease; IPF = idiopathic pulmonary fibrosis; MDT = multidisciplinary team; PFT = pulmonary function test; PHT = pulmonary hypertension | Mikolasch, T. A., Garthwaite, H. S., & Porter, J. C. (2017). Update in diagnosis and management of interstitial lung disease . Clinical medicine (London, England), 17(2), 146–153. https://doi.org/10.7861/clinmedicine.17-2-146

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