Association of chronic and acute inflammation of the mucosa-associated lymphoid tissue with psychiatric disorders and suicidal behavior

Immune dysregulation due to chronic inflammation is a hypothesized risk factor underlying psychiatric disorders and suicidal behavior. Whether tonsillectomy and acute appendicitis used, respectively, as proxies for chronic and acute inflammation within the mucosa-associated lymphoid tissue (MALT) are associated with psychiatric disorders and suicidal behavior is currently unknown. A birth cohort study was conducted including 3,052,875 individuals born in Sweden between 1973 and 2003. We identified 210,686 individuals ever exposed to tonsillectomy and 86,928 individuals ever exposed to acute appendicitis, as well as 317,214 clusters of siblings discordant for tonsillectomy, and 160,079 sibling clusters discordant for acute appendicitis. Outcomes were an aggregate risk of ‘any psychiatric disorder’, ‘any suicidal behavior’, 12 individual psychiatric disorders, suicide attempts and deaths by suicide. Tonsillectomy was associated with increased odds of ‘any psychiatric disorder’ (adjusted odds ratio [aOR] = 1.39; 95% confidence interval (CI) = 1.38–1.41) and ‘any suicidal behavior’ (aOR = 1.41; 95% CI = 1.37–1.44), and most individual disorders. Acute appendicitis also increased the odds of ‘any psychiatric disorder’ and ‘any suicidal behavior’ (aOR = 1.23; 95% CI = 1.20–1.25, and aOR = 1.32; 95% CI = 1.28–1.37, respectively). Exposure to both tonsillectomy and appendicitis was associated with the highest odds of ‘any psychiatric disorder’ (aOR = 1.70; 95% CI = 1.59–1.82) and ‘any suicidal behavior’ (aOR = 1.90; 95% CI = 1.70–2.12). In sibling comparisons, the associations were attenuated but remained significant. We conclude that inflammation within the MALT, particularly when chronic, is robustly associated with a broad range of psychiatric disorders and suicidal behavior.