Idiopathic interstitial pneumonia (mnemonic)

Idiopathic interstitial pneumonias (IIPs) are diffuse interstitial lung diseases of unknown cause. A useful mnemonic for the American Thoracic Society-European Respiratory Society (ATS-ERS) classification of IIPs is:

• All Idiopathic Chronic Lung Disease aRe Nonspecifically Patterned

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.

Mnemonic

• A: acute interstitial pneumonia (AIP). The only acute process in the list.
• I: idiopathic pulmonary fibrosis / usual interstitial pneumonia (IPF / UIP)
• C: cryptogenic organizing pneumonia (COP)
• L: lymphoid interstitial pneumonia (LIP)
• D: desquamative interstitial pneumonia (DIP)
• R: respiratory bronchiolitis–associated interstitial lung disease (RB-ILD)
• N: non-specific interstitial pneumonia (NSIP)
• P: pleuroparenchymal fibroelastosis (PPFE)

The first two, AIP and IPF/UIP, have a very poor prognosis. The next in the list, COP, is associated with a 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 an equal gender distribution.

The following two, DIP and RB-ILD, are at the extreme opposite ends of a spectrum, associated with smoking, with good response to smoking cessation.

PPFE has a relatively poor prognosis, with frequent infectious complications and associated pneumothorax.

One caveat: the word chronic in the mnemonic should be taken with a pinch of salt. Some of the entities may have a subacute presentation, and one, AIP, presents acutely.