Characteristics and disease activity of early interstitial lung disease in subjects with true parenchymal abnormalities in the posterior subpleural aspect of the lung

Study objectives: To evaluate characteristics or disease activity of early interstitial lung disease (ILD) in subjects with true parenchymal abnormalities in the posterior subpleural aspect of the lung. Patients and methods: This study enrolled 14 subjects with dependent densities that disappeared on helical CT obtained with the subject prone (control group) and 7 subjects with true parenchymal abnormalities that remained unchanged on prone CT image but were not detectable on chest radiographs (true abnormalities group). Pulmonary function tests and serum markers for idiopathic lung fibrosis as KL-6, surfactant protein D (SP-D), and surfactant protein A (SP-A) in the two groups were evaluated. Results: In the true abnormalities group, curvilinear subpleural lines or thickened interlobular and intralobular lines were observed more frequently in the lower lung fields. Diffusing capacities of the lung for carbon monoxide (15.3 +/- 3.5 mL/min/mm Hg vs 18.8 +/- 3.7 mL/min/mm Hg, p = 0.0493) were lower, and KL-6 (607 +/- 297 U/mL vs 318 +/- 143 U/mL, p = 0.0090), SP-A (59 +/- 24 ng/mL vs 34 +/- 12 ng/mL, p = 0.0207), and SP-D (112 +/- 54 ng/mL vs 42 +/- 24 ng/mL, p = 0.0028) were higher in the true abnormalities group than in the control group (+/- SD). Conclusion; True parenchymal abnormalities in the posterior subpleural aspect of the lung may indicate early ILD activity.