Development and validation of a radiological diagnosis model for hypersensitivity pneumonitis

Abstract

High-resolution computed tomography (HRCT) may be useful for diagnosing hypersensitivity pneumonitis. Here, we develop and validate a radiological diagnosis model and model-based points score.Patients with interstitial lung disease seen at the University of Michigan Health System (derivation cohort) or enrolling in the Lung Tissue Research Consortium (validation cohort) were included. A thin-section, inspiratory HRCT scan was required. Thoracic radiologists documented radiological features.The derivation cohort comprised 356 subjects (33.9% hypersensitivity pneumonitis) and the validation cohort comprised 424 subjects (15.5% hypersensitivity pneumonitis). An age-, sex- and smoking status-adjusted logistic regression model identified extent of mosaic attenuation or air trapping greater than that of reticulation ("MA-AT>Reticulation"; OR 6.20, 95% CI 3.53-10.90; p<0.0001) and diffuse axial disease distribution (OR 2.33, 95% CI 1.31-4.16; p=0.004) as hypersensitivity pneumonitis predictors (area under the receiver operating characteristic curve 0.814). A model-based score >2 (1 point for axial distribution, 2 points for "MA-AT>Reticulation") has specificity 90% and positive predictive value (PPV) 74% in the derivation cohort and specificity 96% and PPV 44% in the validation cohort. Similar model performance is seen with population restriction to those reporting no exposure (score >2: specificity 91%).When radiological mosaic attenuation or air trapping are more extensive than reticulation and disease has diffuse axial distribution, hypersensitivity pneumonitis specificity is high and false diagnosis risk low (<10%), but PPV is diminished in a low-prevalence setting.

Figure 1.

Derivation Cohort (University of Michigan/UMHS) Patient Flow Diagram * Includes those with ILD diagnosis confirmed by HRCT only (i.e. “Definite UIP” HRCT pattern) and those unwilling or unable to undergo diagnostic biopsy ** Excluded diagnoses include primary cystic lung disease, PAP, airway or pulmonary vascular disease without ILD, drug induced lung disease, infection, and other non-ILD diagnoses (congestive heart failure, etc). *** Of included patients identified from the ICD-9 search alone, 23 HP and 7 control patients had chart documentation of multidisciplinary case review which occurred prior to creation of a searchable database of conference minutes. COP=Cryptogenic Organizing Pneumonia; RB-ILD=Respiratory Bronchiolitis-Interstitial Lung Disease; NSIP=Nonspecific Interstitial Pneumonia; CTD-ILD=Connective tissue disease associated ILD; DIP=Desquamative Interstitial Pneumonia; PLCH=Pulmonary Langerhans Cell Histiocytosis; HRCT=High Resolution Computed Tomography. HRCT=High Resolution Computed Tomography

Figure 2.

Validation (LTRC) Cohort Patient Flow Diagram COP=Cryptogenic Organizing Pneumonia; RB-ILD=Respiratory Bronchiolitis-Interstitial Lung Disease; NSIP=Nonspecific Interstitial Pneumonia; CTD-ILD=Connective tissue disease associated ILD; DIP=Desquamative Interstitial Pneumonia; PLCH=Pulmonary Langerhans Cell Histiocytosis; HRCT=High Resolution Computed Tomography

Figure 3.

Representative Images from two patients with hypersensitivity pneumonitis and HP-HRCT Diagnosis Score of 3 Panels A, B, and C are inspiratory coronal reconstruction, inspiratory axial supine, and expiratory axial supine images, respectively, from a subject with fibrotic HP. Disease is diffusely distributed in the axial direction (white arrows). An example of reticulation is shows in the box, and asterisks (*) mark regions of relatively decreased attenuation (mosaic attenuation) on the inspiratory image (panel B) and air trapping on the expiratory image (Panel C). Panels D, E, and F are inspiratory coronal reconstruction, inspiratory axial supine, and expiratory axial supine images, respectively, from a subject with non-fibrotic HP. Disease is diffusely distributed in the axial direction (white arrows). Asterisks (*) mark regions of relatively decreased attenuation (mosaic attenuation) on the inspiratory image (panel E) and air trapping on the expiratory image (Panel F).