Alveolar Clearance of 99mTc-DTPA Aerosol in the Evaluation of Lung Involvement in 190 Patients with Systemic Sclerosis

Inhaled 99mTc-DTPA alveolar clearance has previously shown to be abnormal in systemic sclerosis (SSc) patients with fibrosing alveolitis and may be useful in predicting the clinical course of parenchimal disease. There is also evidence that alveolar clearance may be abnormal before any other pulmonary evaluation. The aim of this study is to evaluate the alveolar clearance in a large cohort of SSc patients and to compare it to high resolution computed tomography (HRCT) lung score and respiratory function tests (PFTs) including CO diffusion (DLCO).We studied 190 consecutive non smoking SSc patients (179 females and 11 males), with a mean age of 56 years (aging 23-79). All pts underwent 99mTc-DTPA clearance using a commercial available jet nebulizer (Venticis, CIS). The data were collected dinamically with a dual head camera (Philips Vertex) and the activity/time curves by both lungs were generated. The best exponential fit of both curves in the first 15 minutes were calculated. All patients underwent to PFTs and HRCT. The lung scan were scored according to Warrick et al (J Rheumatol. 1991;18:1520-8).Using Pearsons test for paired data we found highly significant correlations between alveolar clearance and HRCT score (p < 0.00000, r = -0.31), and between accelerated clearance and reduced DLCO (p = 0.0003, r = 0.26), and between HRCT and DLCO (p = 0.00000, r = -0.41). In our large number of patients we confirm previously published data of a total score of 8 as the minimum level to consider HRCT abnormalities as predictive of pulmonary disease. At this value the corresponding 99mTc-DTPA alveolar clearance half time resulted of 60 minutes and DLCO resulted of 78%.Moreover 24 of 131 patients (18%) with normal HRCT total score (< 8) had an accelerated alveolar clearance.The significant correlation between alveolar clearance with both HRCT total score and DLCO demostrated the utility of this procedure in the evaluation of lung involvement in SSc patients. In our opinion the main application of this test is in the study of early signs of active lung involvement (alveolitis), even in the patients with normal HRCT and PFTs. In conclusion, our results show that alveolar clearance seem to be an early index of alveolitis and this offer the opportunity, together with the other procedures, for a early recognition and treatment of patients with active disease.