Association between tonsillitis and newly diagnosed ankylosing spondylitis: A nationwide, population-based, case-control study

Objectives
To investigate the association between tonsillitis and the risk of newly diagnosed ankylosing spondylitis (AS).
Methods
We used 2003–2012 data from Taiwan’s National Health Insurance Research Database to conduct this nationwide, population-based, case-control study. We identified AS patients newly diagnosed between 2005 to 2012 as the study group and selected age, sex and index-year matched (1:6) non-AS individuals as controls. The association between tonsillitis and risk of newly diagnosed AS was determined by calculating odds ratios (ORs) with 95% confidence intervals (CIs) using conditional logistic regression analysis.
Results
We identified 37,002 newly diagnosed AS cases and 222,012 matched non-AS controls. Patients with AS were more likely to have tonsillitis (aOR 1.46, 95% CI 1.43–1.50), appendicitis (aOR 1.29, 95% CI 1.13–1.48) and periodontitis (aOR 1.35, 95% CI 1.31–1.38) than non-AS control subjects. The association between tonsillitis and AS was consistent using varying definitions for tonsillitis, and we further found that a high frequency of visits for tonsillitis, a high medical cost for tonsillitis and a long interval between diagnosis were associated with newly diagnosed AS in a dose-response manner. Furthermore, the association between tonsillitis and AS appeared to be stronger in females (aOR 1.59, 95% CI 1.53–1.65) than those in males (aOR 1.39, 95% CI 1.35–1.44).
Conclusions
The present study revealed an association between AS risk and prior tonsillitis and indicates the need for vigilance of AS-associated symptoms in patients who had been diagnosed with tonsillitis, particularly in females.