All Idiopathic Chronic Lung Diseases aRe Nonspecific
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Idiopathic interstitial pneumonias (IIPs) are diffuse interstitial lung diseases of unknown cause. They are characterized by infiltration of the interstitial compartment with inflammatory cells.
"All Idiopathic Chronic Lung Diseases aRe Nonspecific" is a mnemonic for the American Thoracic Society-European Respiratory Society classification of IIPs. The mnemonic reflects the frustration of trying to differentiate them on plain film. Indeed, diagnosis depends on HRCT findings, as well as clinical presentation. Even then, some cases require lung biopsy for definitive diagnosis.
One caveat: The word chronic in the mnemonic should be taken with a grain of salt. Some of the entities may have a subacute presentation, and one, AIP, presents acutely.
- Acute interstitial pneumonia (AIP). The only acute process in the list.
- Idiopathic pulmonary fibrosis/usual interstitial pneumonia (IPF/UIP)
- Cryptogenic organizing pneumonia (COP), formerly bronchiolitis obliterans organizing pneumonia
- Lymphoid interstitial pneumonia (LIP)
- Desquamative interstitial pneumonia (DIP)
- Respiratory bronchiolitis–associated interstitial lung disease (RB-ILD)
- Non-specific interstitial pneumonia (NSIP)
The first two, AIP and IPF/UIP, have very poor prognosis. The next in the list, COP, is associated with good response to steroids and good prognosis. LIP is more common in women (think "LIPstick"), in contrast to the others, which are either more common in men or have equal gender distribution.
The following two, DIP and RB-ILD, are at extremes of a spectrum, are associated with smoking, and have good response with smoking cessation.