Objectives To identify the spectrum of abnormalities seen on thoracic High Resolution Computed Tomography (HRCT) in patients with ankylosing spondylitis (AS), and to look for correlations with clinical findings, plain radiography and pulmonary function testing.

Methods 28 patients with AS meeting the modified New York criteria and without history of respiratory symptoms were enrolled prospectively: 25 men (89.2%) and 3 women with mean age of 37.8 (9.1) years [17–66] and mean disease duration of 7.8 (4.6) years [0.4–19]. All patients underwent posteroanterior plain chest radiography, HRCT and pulmonary function tests.

Results HRCT revealed abnormalities in 17 patients (60.7%): these included interstitial lung disease (n = 2), paraseptal emphysema (n = 2), apical fibrosis (n = 2), bronchiectasis (n = 1), and non-specific interstitial lung disease (n = 11). Plain radiography was abnormal in only 2 cases. Comparison between patients with and without defined thoracic HRCT abnormalities showed no differences in age, sex, disease duration, history of smoking, radiological scores (syndesmophytes score, BASRI) or ESR but showed significant statistical difference in symptomatic severity parameters (Schöber, BASMI, BASDAI). Pulmonary function tests showed a restrictive process in four patients in whom three had an abnormal chest HRCT and an obstructive process in two patients in whom one had emphysema and apical fibrosis on chest HRCT.

Conclusion This study, which describes thoracic HRCT findings in patients with AS and without respiratory symptoms, confirms the high prevalence of a spectrum of abnormalities undetectable on standard plain radiography.