CT Features of the Usual Interstitial Pneumonia Pattern: Differentiating Connective Tissue Disease-Associated Interstitial Lung Disease From Idiopathic Pulmonary Fibrosis

Abstract

Objective: A substantial proportion of cases of usual interstitial pneumonia (UIP) are due to connective tissue disease (CTD)-associated interstitial lung disease (ILD). The purpose of this study was to determine whether specific CT findings can help differentiate a UIP pattern of CTD-ILD from a UIP pattern of idiopathic pulmonary fibrosis (IPF) and whether these signs are associated with survival.

Materials and methods: Adults visiting an ILD clinic from 2006 to 2015 enrolled in a research registry with a multidisciplinary diagnosis of CTD-ILD or IPF and a UIP pattern at high-resolution CT were included in the study. In these subjects with CT findings of UIP due to either IPF or CTD-ILD, three CT findings anecdotally associated with CTD-ILD were assessed for diagnostic accuracy: the "straight-edge" sign, the "exuberant honeycombing" sign, and the "anterior upper lobe" sign. Survival assessments were performed with univariate and multivariable techniques.

Results: The subjects included 63 patients who had CTD-ILD and 133 patients who had IPF with a UIP pattern at CT. All three CT signs were significantly more common in subjects with CTD-ILD than those with IPF (prevalence, 22.2-25.4% for CTD-ILD, 6.0-12.8% for IPF; p = 0.028 to < 0.001). The highest specificity (94.0%) and sensitivity (25.4%) were seen for the straight-edge sign. No CT sign was associated with survival in multivariable analysis.

Conclusion: Although UIP is usually associated with IPF, the index of suspicion for CTD-ILD should be raised in the care of patients with any of the three CT signs. A thorough workup for CTD-ILD should be pursued, including referral to the rheumatology department.

Keywords: connective tissue disease; idiopathic pulmonary fibrosis; survival; usual interstitial pneumonia.

Fig. 1—

65-year-old woman with connective tissue disease. A and B, Axial (A) and sagittal (B) unenhanced chest CT images show substantial degree of reticulation, traction bronchiectasis and bronchiolectasis, and honeycombing within upper lobes, mostly concentrated in anterior aspect consistent with anterior upper lobe sign.

Fig. 2—

52-year-old man with connective tissue disease. A and B, Axial (A) and sagittal (B) unenhanced chest CT images show substantial degree of reticulation and subpleural honeycombing within upper lobes, mostly concentrated in anterior aspect consistent with anterior upper lobe sign.

Fig. 3—

61-year-old woman with known connective tissue disease. A and B, Axial unenhanced chest CT images show peripheral- and basilar-predominant pulmonary fibrosis pattern characterized primarily by florid honeycombing consistent with exuberant honeycombing sign.

Fig. 4—

57-year-old woman with known connective tissue disease. A and B, Axial unenhanced chest CT images show peripheral- and basilar-predominant pulmonary fibrosis pattern characterized primarily by florid honeycombing consistent with exuberant honeycombing sign.

Fig. 5—

49-year-old woman with connective tissue disease. Coronal unenhanced chest CT image shows basilar-preponderant pulmonary fibrosis characterized by ground-glass opacity and reticulation and traction bronchiolectasis. Along lateral aspect of lungs, fibrosis does not extend superiorly along chest wall but rather forms fairly straight interface between fibrosis and normal lung orthogonal to lateral chest wall surface, consistent with straight-edge sign.

Fig. 6—

31-year-old man with connective tissue disease. Coronal unenhanced chest CT image shows basilar-preponderant pulmonary fibrosis characterized mainly by large degree of honeycombing (exuberant-honeycombing sign). Along lateral aspect of lungs, fibrosis does not extend superiorly along chest wall but rather forms fairly straight interface between fibrosis and normal lung orthogonal to lateral chest wall surface, consistent with straight-edge sign.

Fig. 7—

Kaplan-Meier survival curves for connective tissue disease (CTD) and idiopathic pulmonary fibrosis (IPF) (p = 0.016).