Journal Club of Boston Medical Center for Radiology Nonspecific Interstitial Pneumonia and Usual Interstitial Pneumonia: Comparative Appearances at and the Diagnostic Accuracy of Thin-Section CT; Radiology December 2001

Abstract

WHAT IS THE QUESTION BEING ASKED? In patients clinically diagnosed with “interstitial pulmonary fibrosis” can thin-section CT distinguish between Nonspecific Interstitial Pneumonia (NSIP) and Usual Interstitial Pneumonia (UIP) histologic subtypes? WHY IS THIS IMPORTANT? The different histologic subtypes of idiopathic pulmonary fibrosis have different prognoses. Being able to distinguish between the various types based on thin-section CT would theoretically predict patient prognosis better than simply giving a more generic diagnosis of IPF. 4 HISTOLOGICAL SUBTYPES OF CLINICALLY DIAGNOSED IDIOPATHIC PULMONARY FIBROSIS Usual Interstitial Pneumonia (UIP) – most common. Bad prognosis. Nonspecific interstitial pneumonia (NSIP) – Best prognosis Desquamative interstitial pneumonia (DIP) Acute interstitial pneumonia (AIP) WHAT IS THE BACKGROUND WORK? The technology of thin-section CT. Not a new invention, but not ancient either The establishment of various histological subtypes and diagnostic criteria of IPF. The discovery that different histopathologic subtypes carry different prognoses. WHAT IS THE NULL HYPOTHESIS? The null hypothesis states that thin-section CT is not capable of distinguishing the various subtypes of IPF. WHO IS THE TEST POPULATION? Patients who were given the diagnosis of Idiopathic pulmonary fibrosis by clinical grounds: (bibasilar crackles, restrictive defect by PFTs, absence of known cause of IPF.) Of these, some received the diagnosis of either NSIP or UIP by lung biopsy. This group was further refined into a group that underwent thin-section CT scan within 12 months of biopsy. 53 patients were included –all 53 had thin-section CT and lung biopsy with a histologic diagnosis of either UIP or NSIP, and all were diagnosed with IPF based on clinical grounds. WHAT ARE THE METHODS USED? PATHOLOGY: 2 pathologists, basing final diagnosis on predominant histologic findings. Certain histopath criteria was given for the diagnosis of either UIP or NSIP. NSIP patients were further subdivided into cellular or fibrotic subtypes. Indeterminate cases settled by concensus. CT SCANNING: 1.5mm slices, 100 msec acquisition, same w/l SCORING OF CT SCANS: 2 staff chest radiologists and 2 chest fellows scoring the Journal Club of Boston Medical Center for Radiology Nonspecific Interstitial Pneumonia and Usual Interstitial Pneumonia: Comparative Appearances at and the Diagnostic Accuracy of Thin-Section CT; Radiology December 2001 2 of 4 scans independently, without clinical information. They were asked to categorize these as either UIP or NSIP based on thin-section criteria in the literature. NSIP further subclassified into cellular or fibrotic types. Readers asked to assess the lung parenchymal abnormalities : ground glass, reticular or mixed. If reticular, they were asked to score the fineness or coarseness of the reticular pattern. Observers were asked to score the location of abnormality. Degree of confidence was rated as “possible” or “confident.” STATISTICAL ANALYSIS: Sample size of 53 as described above Sensitivity/specificity/accuracy calculations