Is the enemy from within?

Abstract

Andersson et al. conducted a population-based case-control study to assess the relationship between appendectomy and the development of ulcerative colitis (UC). All patients in Sweden with hospital discharge diagnoses that included appendectomies between 1964 and 1993 were identified from the national Inpatient Register. Only those who were younger than 50 at the time of surgery were included. Patients were divided into groups according to their discharge diagnoses, which included perforated appendicitis, nonperforated appendicitis, nonspecific abdominal pain, and mesenteric lymphadenitis. Community controls without histories of appendectomies were matched in a 1:1 fashion based on age, sex, and township of residence. Patients were excluded if they had diagnoses of UC at or before appendectomies, UC was diagnosed within 1 yr after the appendectomy, or there was less than 1 yr of follow-up. Follow-up was done until the diagnosis of UC was made, death, or the study end of December 31, 1995. The diagnosis of UC was established by referencing the same Inpatient Register. A total of 212,963 cases of appendicitis with similar controls were identified, with a follow-up of >5 million person-years. Seven hundred fourteen patients were diagnosed with UC. Overall, patients with histories of appendectomies had a significantly lower incidence of UC, with an incidence rate ratio (IRR) of 0.74 (95% CI = 0.64–0.86). This relationship of a protective effect was true when the discharge diagnosis was acute appendicitis (IRR = 0.75, 95% CI = 0.62–0.87) or mesenteric lymphadenitis (IRR = 0.48, 95% CI = 0.27–0.83), but for only those patients younger than 20. A discharge diagnosis of nonspecific abdominal pain was not associated with a protective effect. Cox proportional-hazards regression modeling resulted in similar findings, with the addition of female sex as a significant covariate to the model. A separate analysis was performed for patients who had surgery before the age of 20 and those 20 or older to assess the relation in the two age groups. Patients who underwent surgery for appendicitis before the age of 20 had a lower risk of UC than controls (IRR = 0.42, 95% CI = 0.31–0.57); those older than 20 had the same risk as controls. The authors concluded that in this large population-based study they were able to confirm an inverse relation between appendectomy and UC. This relation was confined to appendectomy in young patients with inflammation of the appendix or mesenteric lymph nodes.