Usual interstitial pneumonia (UIP): a clinically significant pathologic diagnosis.

This editorial focuses on common issues that surround the diagnosis of usual interstitial pneumonia (UIP), a clinically significant pathologic diagnosis. Most of these issues stem from conflation of the pathologically defined entity UIP with the clinically defined entity IPF. A pathologic or radiologic diagnosis of UIP is required for the clinical/multidisciplinary diagnosis of idiopathic pulmonary fibrosis (IPF) but it has also been described in several other clinical settings. I offer my viewpoint on 5 important questions. 1. Is UIP a diagnosis or a "pattern"? ANSWER: UIP is a pathologic diagnosis and is better conceptualized as a "pattern" than as a specific clinical entity. Since all cases of UIP require pattern recognition, adding the word "pattern" to UIP is redundant. 2. Is pathology the gold standard for UIP? ANSWER: Yes. 3. How do you "prove" etiology of a given case of UIP? ANSWER: "Soft" histologic features can raise the possibility of certain etiologies but the final determination of etiology comes from the multidisciplinary team. With few exceptions, there are no findings pathognomonic for any etiology in UIP. 4. Does UIP imply IPF? ANSWER: No. 5. What should we do when pathology and HRCT are discordant? ANSWER: This depends on the specifics of the discrepancy. When HRCT suggests a non-UIP diagnosis such as NSIP and histology shows UIP, histology has been shown to predict prognosis in multiple studies. In other settings, the radiologic impression based on HRCT is often proven to be incorrect by the histologic findings.