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 symptomless patients with connective tissue disease (CTD), we applied factorial analysis to determine the relationship among the factors. A selected cohort of 71 non-smoking patients with a confirmed diagnosis of CTD [24 with primary Sjögren's syndrome (pSS), 21 with systemic sclerosis (SS), 20 with rheumatoid arthritis (RA) and six with polymyositis/ dermatomyositis (PM/DM)] were identified. The diagnostic techniques included pulmonary function tests, bronchoalveolar lavage (BAL), chest radiographs and high-resolution computed tomography (HRCT). Disease extent and severity were assessed by a radiological and HRCT grading system. Three factors, accounting for 67% of the total variance, 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 BAL and HRCT ground-glass score). The third factor (12.6% of variance) represents a ventilatory function pattern (forced vital capacity, total lung capacity and forced respiratory volume in 1 s). The negative correlation between the fibrotic lung pattern and ventilatory function pattern, but not with the inflammatory lung pattern, suggests the presence of a significant derangement of the alveolar structures. In conclusion, application of factor analysis reveals various lung disease patterns in patients with CTD that might have different prognostic implications.