Pulmonary structure and function analysis in systemic sclerosis : clinical assessment of complicating interstitial lung disease and pulmonary vasculopathy

Abstract

In SSc, we evaluated the optimal percentile density score in SSc by quantitative CT densitometry, against pulmonary function. Lung volumes and the nth percentile density (between 1 and 99%) of the entire lungs were calculated from CT histograms. The nth percentile density is defined as the threshold value of densities expressed in Hounsfield units. A prerequisite for an optimal percentage was its correlation with baseline DLCO% predicted. Regression analysis for the relation between DLCO% predicted and the nth percentile density was optimal at 85% (Perc85). There was significant agreement between Perc85 and DLCO %predicted and FVC% predicted. Of interest, two patients showed a marked change in Perc85 over a two year period, but the localisation of change differed clearly. We conclude that we identified Perc85 as optimal lung density parameter, which correlated significantly with DLCO and FVC, confirming a lung parenchymal structure-function relation in SSc. This provides support for future studies to determine whether structural changes do precede lung function decline.