What’s the difference between IPF and UIP?

As a medical student, I found the various interstitial lung diseases (ILDs) to be horribly confusing. The most common idiopathic ILD is idiopathic pulmonary fibrosis, which is often used interchangeably with usual interstitial pneumonia (UIP). Is there a difference?

Well, yes. UIP is a histopathological description of a lung biopsy that has a specific pattern of fibrosis. (It’s a horrible name, but I was recently told that they tried to change it a decade or two ago and couldn’t come up with anything better.) UIP might also be used to refer to specific findings on high-resolution CT that has a very high correlation with UIP on histopathology. High-res CT is now so good that you usually don’t need the biopsy to know that a patient has UIP.

IPF, on the other hand, is what you call someone with UIP in the lungs if you don’t know why they have it. There are many things that cause UIP on CT and biopsy, including chronic hypersensitivity pneumonitis, connective tissue disorders, and drugs. If the patient doesn’t have any of those diseases or exposures, then it’s said to be idiopathic, and you call it idiopathic pulmonary fibrosis.

This distinction is actually very important, because IPF has a very poor prognosis and has no good disease-modifying treatments, whereas some of the other causes of UIP can be treated.

And now that you understand the difference between IPF and UIP, I’d like to add cryptogenic fibrosing alveolitis to your vocabulary—the fancy British way of saying IPF.

Read more: Idiopathic Pulmonary Fibrosis in Chapter 315: Interstitial Lung Diseases, Harrison’s Principles of Internal Medicine 19e.

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