usual interstitial pneumonia

Usual interstitial pneumonia, almost always shortened to UIP, is a particular pattern of lung scarring rather than a disease in its own name. Think of it as a recognizable fingerprint that fibrosis can leave behind. When radiologists and pathologists see this fingerprint, it strongly steers the diagnosis, most often toward idiopathic pulmonary fibrosis.

The UIP pattern has hallmark features: scarring that is patchy and uneven, worst in the lower and outer parts of the lungs, with areas of normal lung sitting next to dense fibrosis. On high-resolution CT this appears as subpleural, basal honeycombing and traction bronchiectasis. Under the microscope, the same heterogeneity shows up as old scar alongside small foci of active fibrosis.

Importantly, UIP is a pattern, not a cause. While it is the defining pattern of IPF, the very same appearance can arise in connective-tissue-disease ILD, chronic hypersensitivity pneumonitis, asbestosis, and certain drug reactions. So recognizing UIP narrows the field but does not finish the diagnosis; the clinical context must still be weighed.

Modern guidelines grade CT findings as typical UIP, probable UIP, indeterminate, or suggestive of an alternative diagnosis. A typical or probable UIP appearance in the right clinical setting can confirm IPF without surgery, which spares many patients an invasive biopsy.