There is histopathological evidence that, in certain inflammatory disorders involving the smaller airways, extension of the inflammatory process may occur distally into the respiratory bronchioles, alveolar ducts and alveoli (1,2). The objective of this study was to perform a non-invasive evaluation of the possible involvement of gas exchanging regions of the lung in obliterative
bronchiolitis presenting with severe airways obstruction. We measured the clearance of
technetium 99m-labelled
diethylene triamine penta-
acetate (99m Tc-DTPA) with time from the lungs to the blood, in 11 normal, non-smoking subjects (mean age 30 years), ten non-smoking patients with
cryptogenic fibrosing alveolitis (CFA, mean age 57 years) and ten patients who were non-smokers with obliterative
bronchiolitis (mean age 51 years). There was a substantial increase in clearance in patients with CFA, (mean T1/2 19.9 min), compared with either patients with obliterative
bronchiolitis (mean T1/2 52.2 min; mean difference 32.3; 95% confidence intervals (CI) 18.40; P less than 0.001) or normal controls (mean T1/2 84.3; mean difference 64.4; 95% CI 55, 74; P less than 0.001). Clearance was also significantly faster in patients with obliterative
bronchiolitis than in normal controls (mean difference 32.1; 95% CI 18.48; P less than 0.001). Peripheral deposition of 99m
Tc-DTPA was uniform in normal subjects and patients with CFA, but patchy in patients with obliterative
bronchiolitis, possibly resulting from altered patterns of ventilation associated with patchy distribution of
bronchiolitis within affected lungs. Increased clearance of 99m
Tc-DTPA from the lungs in these patients suggests that subtle derangement of the alveolar-capillary membrane occurs in adult obliterative
bronchiolitis.