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Appendectomy was associated with a moderately increased risk of developing microscopic colitis, a case-control study from Sweden found.

Among over 14,500 patients, those who previously underwent an appendectomy had an overall higher risk of developing microscopic colitis (adjusted odds ratio [aOR] 1.50, 95% CI 1.40-1.61), and this relationship held true for its subtypes:

• Collagenous colitis: aOR 1.67 (95% CI 1.48-1.88)
• Lymphocytic colitis: aOR 1.42 (95% CI 1.30-1.55)

The risk remained elevated even 10 years after an appendectomy (aOR 1.41, 95% CI 1.30-1.52), and the highest associated risk among patients with complicated appendicitis was seen 5 to 10 years after appendectomy, reported John Maret-Ouda, MD, PhD, of the Karolinska Institutet in Stockholm, and colleagues in .

Furthermore, subanalyses showed that index biopsy within 1 year of appendectomy showed the highest associated risk of microscopic colitis (aOR 3.17, 95% CI 2.05-4.91), which also persisted for its subtypes, and when looking at all cases, the highest associated risk was found less than 1 year after appendectomy with non-complicated appendicitis (aOR 3.36, 95% CI 2.14-5.26).

"Time since appendectomy and severity of appendicitis seem to influence the associated risk," Maret-Ouda's group noted.

Microscopic colitis, an inflammatory bowel disease (IBD), often results in chronic diarrhea. While appendectomy could have an immunomodulating effect on the colon, the link between microscopic colitis and appendectomy has only been examined in two small studies, finding no .

"The pathophysiology of microscopic colitis is thought to be associated with a dysregulated immune response in the gut mucosa, in genetically predisposed individuals, and infiltration of T-helper cells 17 (Th17) in the lamina propria of colon has been observed," the authors explained, adding that appendicitis has been linked to upregulation of the Th17 pathway.

For this study, Maret-Ouda and colleagues examined data from the cohort on 14,520 patients with microscopic colitis who were matched by sex, age, year of biopsy, and residential county to 69,491 controls without microscopic colitis. Of the patients with microscopic colitis, 9,836 had lymphocytic colitis and 4,684 had collagenous colitis. Patients underwent biopsy for microscopic colitis from 1990 to 2017.

Almost half of patients were diagnosed with microscopic colitis at ages 50 to 70 (43.2%), and 72% were women. Only 4.3% of patients with microscopic colitis had been diagnosed with another form of IBD.

Prior to matching, 7.6% of patients with microscopic colitis and 5.1% of controls underwent an appendectomy ≥1 year earlier. Uncomplicated appendicitis was the most common diagnosis.

A post-hoc analysis that stratified patients by age at appendectomy showed similar results across all subgroups.

Maret-Ouda and team acknowledged the possibility of residual confounding and the potential for false diagnoses among those with appendicitis. In addition, the effects of healthcare utilization may have introduced bias.

Since data were not available on lifestyle factors, any potential role in the development of appendicitis or microscopic colitis could not be assessed, they noted.

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