The differing patterns of subclinical pulmonary involvement in connective tissue diseases as shown by application of factor analysis

To explore common patterns of interstitial lung disease (ILD) in symptomles s patients with connective tissue disease (CTD), we applied factorial analy sis to determine the relationship among the factors. A selected cohort of 7 1 non-smoking patients with a confirmed diagnosis of CTD [24 with primary S jogren's syndrome (pSS), 21 with systemic sclerosis (SS), 20 with rheumatoi d arthritis (RA) and six with polymyositis/dermatomyositis (PM/DM)] were id entified. The diagnostic techniques included pulmonary function tests, bron choalveolar lavage (BAL), chest radiographs and high-resolution computed to mography (HRCT). Disease extent and severity were assessed by a radiologica l and HRCT grading system. Three factors, accounting for 67% of the total v ariance, were extracted. The first factor (disease duration, diffusing lung capacity, neutrophils and CD8+ T cells on BAL, radiographic score and HRCT reticular score), with the highest percentage of variance (36.5%), defines a fibrotic lung pattern. The second factor (17.9% of variance) identifies an inflammatory lung pattern (macrophages, lymphocytes and eosinophils on B AL and HRCT ground-glass score). The third factor (12.6% of variance) repre sents a ventilatory function pattern (forced vital capacity, total lung cap acity and forced respiratory volume in 1 s). The negative correlation betwe en the fibrotic lung pattern and ventilatory function pattern, but not with the inflammatory lung pattern, suggests the presence of a significant dera ngement of the alveolar structures. In conclusion, application of factor an alysis reveals various lung disease patterns in patients with CTD that migh t have different prognostic implications.