Abstract
BackgroundAccurate diagnosis of idiopathic pulmonary fibrosis (IPF) is essential to inform prognosis and treatment. In 2018, the ATS/ERS/JRS/ALAT and Fleischner Society released new diagnostic guidelines for usual interstitial pneumonitis (UIP)/IPF, adding Probable UIP as a CT category based on prior studies demonstrating this category had relatively high positive predictive value (PPV) for histopathologic UIP/Probable UIP. This study applies the 2018 ATS/ERS/JRS/ALAT and Fleischner Society guidelines to determine test characteristics of CT categories in academic clinical practice.MethodsCT and histopathology were evaluated by three thoracic radiologists and two thoracic pathologists. Comparison of consensus categorization by the 2018 ATS and Fleischner Society guidelines by CT and histopathology was performed.ResultsOf patients with CT UIP, 87% (PPV, 95% CI: 60–98%) had histopathologic UIP with 97% (CI: 90–100%) specificity. Of patients with CT Probable UIP, 38% (PPV, CI: 14–68%) had histopathologic UIP and 46% (PPV, CI: 19–75%) had either histopathologic UIP or Probable UIP, with 88% (CI: 77–95%) specificity. Patients with CT Indeterminate and Alternative Diagnosis had histopathologic UIP in 27% (PPV, CI: 6–61%) and 21% (PPV, CI: 11–33%) of cases with specificities of 90% (CI: 80–96%) and 25% (CI: 16–37%). Interobserver variability (kappa) between radiologists ranged 0.32–0.81.ConclusionsCT UIP and Probable UIP have high specificity for histopathologic UIP, and CT UIP has high PPV for histopathologic UIP. PPV of CT Probable UIP was 46% for combined histopathologic UIP/Probable UIP. Our results indicate that additional studies are needed to further assess and refine the guideline criteria to improve classification performance.
Highlights
Idiopathic pulmonary fibrosis (IPF) is a progressive, often fatal interstitial lung disease (ILD), characterized by a usual interstitial pneumonitis (UIP)-pattern on chest computed tomography (CT) scan and/or histopathologic examination of surgical biopsies [1,2,3]
The descriptions and criteria for the four categories were modified for CT and histopathology to better stratify cases based on the confidence level of UIP diagnosis, and better inform the confidence of idiopathic pulmonary fibrosis (IPF) diagnosis
63 cases were categorized as Alternative Diagnosis by radiology, and 34 cases were categorized as Alternative Diagnosis by histopathology, with the most common alternative diagnosis being chronic hypersensitivity pneumonitis (Additional file 2: Tables S1 and S2)
Summary
Idiopathic pulmonary fibrosis (IPF) is a progressive, often fatal interstitial lung disease (ILD), characterized by a usual interstitial pneumonitis (UIP)-pattern on chest computed tomography (CT) scan and/or histopathologic examination of surgical biopsies [1,2,3]. The ATS/ERS/JRS/ALAT and Fleischner Society separately published updated guidelines for UIP/IPF diagnosis in 2018 [2, 3]. Both guidelines effected very similar changes to CT categorization, expanding the prior system of three categories (UIP, Possible UIP, and Inconsistent with UIP patterns) to the current system of four categories (UIP, Probable UIP, Indeterminate for UIP, and Alternate Diagnosis). Accurate diagnosis of idiopathic pulmonary fibrosis (IPF) is essential to inform prognosis and treatment. In 2018, the ATS/ERS/JRS/ALAT and Fleischner Society released new diagnostic guidelines for usual interstitial pneumonitis (UIP)/IPF, adding Probable UIP as a CT category based on prior studies demonstrating this category had relatively high positive predictive value (PPV) for histopathologic UIP/Probable UIP. This study applies the 2018 ATS/ ERS/JRS/ALAT and Fleischner Society guidelines to determine test characteristics of CT categories in academic clinical practice
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