Serial CT analysis in idiopathic pulmonary fibrosis: comparison of visual features that determine patient outcome

Abstract

Aims: Patients with idiopathic pulmonary fibrosis (IPF) receiving antifibrotic medication and patients with non-IPF fibrosing lung disease often demonstrate rates of annualised forced vital capacity (FVC) decline within the range of measurement variation (5.0%-9.9%). We examined whether change in visual CT variables could help confirm whether marginal FVC declines represented genuine clinical deterioration rather than measurement noise.

Methods: In two IPF cohorts (cohort 1: n=103, cohort 2: n=108), separate pairs of radiologists scored paired volumetric CTs (acquired between 6 and 24 months from baseline). Change in interstitial lung disease, honeycombing, reticulation, ground-glass opacity extents and traction bronchiectasis severity was evaluated using a 5-point scale, with mortality prediction analysed using univariable and multivariable Cox regression analyses. Both IPF populations were then combined to determine whether change in CT variables could predict mortality in patients with marginal FVC declines.

Results: On univariate analysis, change in all CT variables except ground-glass opacity predicted mortality in both cohorts. On multivariate analysis adjusted for patient age, gender, antifibrotic use and baseline disease severity (diffusing capacity for carbon monoxide), change in traction bronchiectasis severity predicted mortality independent of FVC decline. Change in traction bronchiectasis severity demonstrated good interobserver agreement among both scorer pairs. Across all study patients with marginal FVC declines, change in traction bronchiectasis severity independently predicted mortality and identified more patients with deterioration than change in honeycombing extent.

Conclusions: Change in traction bronchiectasis severity is a measure of disease progression that could be used to help resolve the clinical importance of marginal FVC declines.

Keywords: bronchiectasis; idiopathic pulmonary fibrosis; imaging/CT.

Figure 1

Serial axial CT images in patients with idiopathic pulmonary fibrosis. In a 50-year-old male patient who did not receive antifibrotic medication and who demonstrated a >10% annualised FVC decline, images acquired 6 months apart (Ai, ii) show change in traction bronchiectasis categorised as markedly worsened (score=5) by scoring radiologists. In a 62-year-old male patient who received antifibrotic medication (Bi, ii), images acquired 13 months apart show annualised FVC decline between 5.0% and 9.9%, and change in traction bronchiectasis was categorised as mildly worsened (score=4). In a 77-year-old man who did not receive antifibrotic medication (Ci, ii) and who had CTs acquired 15 months apart, change in traction bronchiectasis severity (Score=3) and annualised FVC decline (−5.0% to 4.9%) were both considered stable. Parenchymal changes visible on the CT may reflect disease maturation rather than disease progression. FVC, forced vital capacity.

Figure 2

Spaghetti plot demonstrating longitudinal change in FVC from the time of the baseline CT scan. Patients have been classified as having no change in traction bronchiectasis (red) and change in traction bronchiectasis (blue). The start and end FVC measurements considered in the longitudinal analyses were within 3 months of the respective CT scan dates. FVC, forced vital capacity; TxBx, traction bronchiectasis.