This nationwide, retrospective cohort study of 17088 people provided evidence that ankylosing spondylitis patients aged more than 65 years are more prone to the development of fibromyalgia irrespective of gender.

To investigate the risk of fibromyalgia in ankylosing spondylitis (AS) patients in large study samples.

The data of patients with AS were obtained from the National Taiwan Insurance Research Database (NHIRD) and Longitudinal Health Insurance Database (LHID). The exposure cohort incorporated patients recently diagnosed with AS during 14 years.

People without AS were identified as a comparison cohort following the 1:4 age-sex and 1:2 propensity score matching, and adjustment of the possible confounders. Assessment of adjusted hazard ratio (aHR) of progression of fibromyalgia in AS patients were done. Different age groups and genders were considered to confirm the results.

Out of 17 088 people considered, 5,696 patients had AS (AS cohort) and 11,392 were healthy adults (non-AS cohort). Fibromyalgia prevalence rate (per 1000 person-months) was 0.52 in AS and 0.39 in the non-AS cohort. The aHR of progression of fibromyalgia was 1.32 in AS cohort than the non-AS cohort. 

Older patients (more than 65 years) with AS aged are more likely to suffer from fibromyalgia compared to those without AS. Medical care professionals should be aware of this correlation for the effective management of AS.