Lung function in patients with ankylosing spondylitis. A study of the influence of disease activity and treatment with nonsteroidal antiinflammatory drugs.

Progressive ankylosis of the thoracic skeleton in ankylosing spondylitis (AS) causes restrictive pulmonary function impairment characterized by a reduction in vital capacity (VC). After a wash-out period of 2 weeks, 33 men with active AS were treated with either diflunisal or phenylbutazone according to a double blind randomized design for 12 weeks, followed by an open extension period of 36 weeks. A spirometric study was performed at baseline, Week 12, and Week 48. In the active phase of the disease a correlation was found between VC and chest expansion, whereas neither of these variables was related to the thoracic pain and over-all disease activity. We also found that the VC correlated with the lumbar flexion index, but not with the erythrocyte sedimentation rate or IgA. Although all clinical efficacy variables showed an improvement during treatment with both drugs, no change in VC was found, even in patients with the most restricted ventilatory impairment. We conclude that the VC is not an appropriate variable for the evaluation of short term therapy in AS.