Association between ankylosing spondylitis and chronic obstructive pulmonary disease in Taiwan

One cross-sectional study conducted by Sharif et al. reported that patients with ankylosing spondylitis had a higher proportion of chronic obstructive pulmonary disease than controls (46% versus 18%, P < 0.001) [ ]. After controlling for age, gender, and smoking status, a significant association exists between ankylosing spondylitis and chronic obstructive pulmonary disease (odds ratio 1.225, P = 0.031) [ ]. We are interested in these findings. Currently, the relationship between ankylosing spondylitis and chronic obstructive pulmonary disease has not yet been investigated in Taiwan. We designed a cohort analysis to examine the database of the Taiwan National Health Insurance Program with 23 million persons living in an independent country of Taiwan [ , ]. Subjects aged 20 to 84 years with a new primary diagnosis of ankylosing spondylitis from 2000 to 2012 were selected as the ankylosing spondylitis group based on International Classification of Diseases, Ninth Revision codes (ICD-9 codes 720.0). For every subject with ankylosing spondylitis, 4 sex-matched and age-matched subjects without ankylosing spondylitis were identified as the non-ankylosing spondylitis group. The ankylosing spondylitis group and the non-ankylosing spondylitis group were followed up until a new diagnosis of chronic obstructive pulmonary disease was made (ICD-9 codes 491, 492, 493, and 496) or until the end of 2013.