Purpose: Three different grades of idiopathic pulmonary fibrosis can be identified by HRCT pattern. Patients with predominant ground-glass opacity (grade I) usually improve after treatment and may have a better prognosis. The subjects with a predominant reticular pattern and honeycombing (grade III) have irreversible fibrosis and usually do not improve after immunosuppressive therapy. Nevertheless, these patients may worsen even in the absence of HRCT features of the so-called alveolitis. We investigated the predictive role of some noninvasive imaging methods (HRCT with visual score of disease extent; Gallium scintigraphy; DTPA scintigraphy) in patients with idiopathic fibrosis and a prevalent macroscopic fibrosis at HRCT study.
Material and methods: Fourteen former smokers with grade III idiopathic fibrosis were examined. None of the patients had been treated. They were all submitted to HRCT, lung function studies, Gallium and DTPA scintigraphy, both at presentation (T0) and follow-up sessions (T1: mean one year post-diagnosis). The HRCT extent of disease was evaluated by means of the visual score as the fraction of the total lung volume. The patients were divided into two groups, using a cut-off value of 50%. All the patients underwent a Gallium scintiscan (using a fixation index of 160 as cut-off) and a ventilatory scintigraphy with DTPA-aerosol, with radionuclide clearance assessment. The lung function tests considered were vital capacity (VC), arterial blood oxygen partial pressure (PaO2) and the diffusing lung capacity for carbon monoxide (DLCO).
Results: After one year of follow-up, the HRCT extent score increased (from 46.6% to 50%) and lung function worsened (VC from 66.8% to 63.4% of predicted; DLCO from 37.6% to 27.1%; PaO2 from 77 to 71 mmHg). The patients presenting with HRCT extension score > 50% had a worse lung function at T0 and showed a significant deterioration of PaO2 and HRCT at T1. On the other hand, VC and DLCO significantly worsened in the subjects with HRCT score < 50% at presentation. The patients with a Gallium fixation index > 160 significantly deteriorated in HRCT score, VC and DLCO. Those with Gallium index < 160 had major worsening only for diffusing lung capacity for carbon monoxide. Thirteen of 14 patients had an abnormal value of DTPA clearance at presentation. No variation was observed at T1.
Discussion and conclusions: The majority of patients with idiopathic fibrosis are grade III at presentation. They can further deteriorate both in HRCT extent of disease and lung function impairment. After one year of follow-up HRCT extent score increased in 64% of the patients, with a mean increase of 5%. HRCT worsening was more apparent in the patients with a HRCT score > 50% at presentation. In the remaining patients, the worsening of lung function tests was more apparent than the anatomoradiological changes. DTPA clearance had no predictive value in this series. Gallium scintigraphy was a useful prognostic index. The patients with Gallium fixation index > 160 had better lung function and lower HRCT extent score at T0 but significantly deteriorated at T1. A positive Gallium scan at presentation could be considered a useful index of persisting active "alveolitis" in patients with grade III disease, not visible at HRCT study, due to overwhelming fibrosis. These patients, who were untreated, exhibit quicker radiological and functional worsening.