S1645 Watery Diarrhea in Hashimoto’s Patients? Think Microscopic Colitis—Insights From a National Study

Introduction: Microscopic colitis (MC) causes chronic watery diarrhea that’s often mistaken for irritable bowel syndrome—or even for iatrogenic diarrhea. Because Hashimoto’s thyroiditis is an autoimmune disease with excess immune activity, we investigated whether people with Hashimoto’s are more likely to develop MC. Methods: We performed a cross-sectional analysis of adult discharges in the years 2016-2022 using the NIS. MC cases were identified by validated International Classification of Diseases10CM codes and compared with all other adult hospitalizations. Candidate predictors—including sex, age category (18–45, 46–65, >65 y), Hashimoto’s thyroiditis, smoking, and nonsteroidal anti-inflammatory drug (NSAID) use were evaluated with multivariable survey-weighted logistic regression using STATA 18. Results: We identified an estimated 72,830 hospital stays related to microscopic colitis across the United States. Roughly three-quarters of these patients were women, and about the same proportion were older than 65 years. After controlling for other factors, Hashimoto’s thyroiditis nearly tripled the odds of microscopic colitis (aOR 2.68, 95% CI 1.70–4.21). As expected the strongest predictors of MC were celiac disease (aOR 14.38, 95% CI 11.53–17.94), CKD (aOR 6.63, 95% CI 5.90–7.46), age > 65 years (aOR 5.06, 95% CI 3.97–6.45) and age 46–65 years (aOR 2.72, 95% CI 2.11–3.50), female sex (aOR 2.78, 95% CI 2.58–2.98), IBD (aOR 2.73, 95% CI 2.27–3.28), and RA (aOR 1.72, 95% CI 1.50–1.98). Additional positive associations included lupus (aOR 1.51, 95% CI 1.14–2.00), alcohol use (aOR 1.29, 95% CI 1.07–1.54) and current smoking (aOR 1.30, 95% CI 1.17–1.44). Compared with White patients, all other race categories had significantly lower odds of MC. While recent NSAID use (aOR 1.40, 95% CI 1.23–1.60) modestly increased risk. Compared with adults aged 18–45 years, those aged 46–65 years had about a fivefold increase in risk (aOR 5.18, 95% CI 4.77–5.62), and those older than 65 years showed a twelvefold rise (aOR 12.06, 95% CI 11.18–13.02). Female sex remained an independent predictor, tripling the odds of microscopic colitis (aOR 3.09, 95% CI 2.97–3.21). Conclusion: Hashimoto’s thyroiditis shows a strong, independent link with microscopic colitis. High suspicion is advised when evaluating high-risk groups such as middle-aged females with Hashimoto's for watery diarrhea. Early recognition may prompt targeted evaluation and treatment, improving patient outcomes.