Background: A history of appendectomy is rare in patients with ulcerative colitis. This suggests a protective effect of appendectomy or that appendicitis and ulcerative colitis are alternative inflammatory responses. We sought to characterize this inverse relation further.
Methods: We studied a cohort of 212,963 patients who underwent appendectomy before the age of 50 years between 1964 and 1993 and a cohort of matched controls who were identified from the Swedish Inpatient Register and the nationwide census. The cohort was followed until 1995 for any subsequent diagnosis of ulcerative colitis.
Results: Patients who underwent appendectomy for appendicitis and mesenteric lymphadenitis had a low risk of ulcerative colitis (for patients with perforated appendicitis, the adjusted hazard ratio was 0.58 [95 percent confidence interval, 0.38 to 0.87]; for those with nonperforated appendicitis it was 0.76 [95 percent confidence interval, 0.65 to 0.90]; and for those with mesenteric lymphadenitis it was 0.57 [95 percent confidence interval, 0.36 to 0.89]). In contrast, patients who underwent appendectomy for nonspecific abdominal pain had the same risk of ulcerative colitis as the controls (adjusted hazard ratio, 1.06; 95 percent confidence interval, 0.74 to 1.52). For the patients who had appendicitis, an inverse relation with the risk of ulcerative colitis was found only for those who underwent surgery before the age of 20 years (P<0.001).
Conclusions: Appendectomy for an inflammatory condition (appendicitis or lymphadenitis) but not for nonspecific abdominal pain is associated with a low risk of subsequent ulcerative colitis. This inverse relation is limited to patients who undergo surgery before the age of 20 years.