Objectives To analyse the subclinical pulmonary involvement in a series of patients with ankylosing spondylitis (AS).

Methods Prospective study analysing 52 patients with the diagnosis of AS according to the modified New York criteria. The patients were asymptomatic about lung complaints and were submitted to a pulmonary investigation that included plain chest radiography, pulmonary function test (PFT) and thoracic high-resolution computed tomography (HRCT). The results were compared with sex, race, dorsal spine involvement, thoracic diameter, smoking status and HLA-B27. There was predominance of male (81%), Caucasoid (75%), non-smoking (64%) and positive HLA-B27 (75%) patients, with dorsal spine involvement in 58%. Mean age was 40 years and mean disease duration was 16 years.

Results There were five patients (10%) with an altered plain chest radiography. PFT presented a restrictive pattern in 52% of the patients. Thoracic HRCT showed abnormalities in 21 patients (40%), predominantly nonspecific linear parenchymal opacities (19%), lymphadenopathy (12%), emphysema (10%), bronquiectasis (8%) and pleural involvement (8%). Male sex was statistically associated with dorsal involvement (p = 0.012). Non-Caucasoid race was associated with bronquiectasis (p = 0.044) and pleural involvement (p = 0.044) at the thoracic HRCT. Smoking patients presented more linear parenchymal opacities (p = 0.026) at the thoracic HRCT. Negative HLA-B27 was associated with an altered plain chest radiography (p = 0.011). Dorsal spine involvement was associated with restrictive pattern at PFT (p = 0.001) and linear parenchymal opacities (p = 0.032) at the thoracic HRCT. A lower thoracic diameter was observed in patients with dorsal spine involvement (p = 0.0001), restrictive pattern at PFT (p = 0.023) and linear parenchymal opacities (p = 0.015) at the thoracic HRCT.

Conclusion Subclinical pulmonary involvement is frequent in AS. The restrictive pattern at PFT is associated with dorsal spine involvement and a low thoracic diameter, whilst the thoracic HRCT presents a series of nonspecific alterations, predominating the linear parenchymal opacities.