Histogram- based analysis in progressive pulmonary fibrosis: relationships between pulmonary functional tests and HRCT indexes

Objectives: To investigate relationships between histogram based high-resolution CT (HRCT) indexes and pulmonary function tests (PFTs) in interstitial lung diseases.Methods: Forty nine patients having baseline and 1 year HRCT examinations and PFTs were investigated. Histogram based HRCT indexes were calculated; strength of associations with PFTs was investigated using Pearson correlation. Patients were divided into progressive and non-progressive groups. HRCT indexes were compared between the two groups using the U test; within each group, baseline and follow up Wilcoxon analysis was performed. Receiver operating characteristic analysis was used for predicting disease progression. Results: At baseline, moderate correlations were observed considering kurtosis and diffusion capacity of the lungs for carbon monoxide (DLCO) (r = 0.54) and skewness and DLCO (r = 0.559), whereas weak but significant correlations were observed between forced vital capacity and kurtosis (r = 0.368, p = 0.009) and forced vital capacity and skewness (r = 0.391, p = 0.005). Negative correlations were reported between HAA% and PFTs (from r = -0.418 up to r = -0.507). At follow up correlations between quantitative indexes and PFTs were also moderate, except for high attenuation area (HAA)% -700 and DLCO (r = -0.397). In progressive subgroup, moderate and strong correlations were found between DLCO and HRCT indexes (r = 0.595 kurtosis, r = 0.672 skewness, r=-0. 598 HAA% -600 and r = -0.626 HAA% -700). At follow up, we observed significant differences between the two groups for kurtosis (p = 0.029), HAA% -600 (p = 0.04) and HAA% -700 (p = 0.02). To predict progression, ROC analysis reported sensitivity of 90.9% and specificity of 51.9% using a threshold value of delta kurtosis <0.03. Conclusion: At one year, moderate correlations suggest that progression could be assessed through HRCT quantification.Advances in knowledge: This study promotes histogram-based HRCT indexes in the assessment of progressive pulmonary fibrosis.