Air Trapping in Primary Sjögren Syndrome: Correlation of Expiratory CT with Pulmonary Function Tests

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Abstract
The purpose of our study was to correlate the extent of air trapping on expiratory CT scans with results of pulmonary function tests (PFTs) in a large group of patients with primary Sjögren syndrome and to determine whether these techniques may be complementary in assessing small airways obstruction. Thirty-four nonsmoking patients with proven primary Sjögren syndrome and 10 healthy nonsmokers underwent paired inspiratory-expiratory thin section CT and PFTs. Expiratory scans were scored for the presence and extent of areas of air trapping. Extent of air trapping was assessed visually and given a score. The functional significance of the extent of air trapping was evaluated in both groups and then correlated with the results of PFTs. Bronchiolar abnormalities were seen in 11 (32%) of 34 patients with primary Sjögren syndrome. On the expiratory CT scans, a mosaic pattern of lung attenuation was identified in 17 patients. Air trapping was found in 44 of 204 lobar observations on the expiratory scans. The median point scale score at end-expiration was 3.6 (20%, Grade 1), ranging from 1 (5.5%, Grade 1) to 9 (50%, Grade 2). The mean total score of air trapping was more prevalent in lower (46/68) lobes (22.4%) than in upper (22/136) lobes (5.3%) (p < 0.001). PFTs were normal in the primary Sjögren syndrome patients as well as the healthy subjects. Air trapping was found more frequently in patients with primary Sjögren syndrome than in the healthy group. Only during exhalation was there evidence of minimal lobular-sized areas or air trapping (Grade 1) in three of the healthy subjects. We did not find any correlation between air trapping and PFTs including the forced expiratory flow rate between 25 and 75% of the forced vital capacity (FEF25-75). Expiratory high resolution CT revealed the extent of bronchiolar disease in patients with primary Sjögren syndrome. We also found that the extent of air trapping did not correlate with PFTs, which suggests the existence of a subclinical bronchiolar inflammatory process that may precede detectable abnormalities in lung function tests.