Long-Term Venous Thromboembolism Risk in Microscopic Colitis

The long-term risk of venous thromboembolism (VTE) in individuals with microscopic colitis (MC) has been evaluated in a nationwide Swedish cohort study. Microscopic colitis is an inflammatory bowel disorder characterized by chronic watery diarrhea despite normal endoscopic findings. While inflammatory bowel disease (IBD) is already known to increase thrombotic risk, there has been limited data regarding VTE risk in MC, despite the shared inflammatory mechanisms and the typically older, comorbidity-prone patient population.

### Study Overview:

The study utilized the ESPRESSO cohort, which included 12,489 adults diagnosed with biopsy-confirmed microscopic colitis (MC) between 1990 and 2017. The cohort encompassed two subtypes of MC: collagenous colitis and lymphocytic colitis. These individuals were matched to 55,809 reference individuals without MC or prior VTE. Participants were followed until 2021 to assess the incidence of VTE events. The study adjusted for demographic factors, comorbidity burden, and celiac disease using Cox proportional hazards models to estimate risk.

### Key Findings:

1. **Increased Risk of VTE:**

• Individuals with MC had a higher incidence of VTE compared to the matched controls (11.3 vs. 8.6 per 1,000 person-years).
• MC was associated with a **21% increased risk of VTE** overall.

2. **Subtypes of MC:**

• The increased VTE risk was similar for both collagenous colitis and lymphocytic colitis subtypes.

3. **Types of VTE Events:**

• Elevated risks were observed for pulmonary embolism, deep vein thrombosis (DVT) of the legs, and other thromboses.

4. **Impact of Disease Severity:**

• Patients treated with **budesonide** (a common treatment for MC) within one year of diagnosis, which served as a marker for more severe disease, had a notably higher risk of VTE.

5. **Subgroup and Sensitivity Analyses:**

• These analyses generally supported the findings, though sibling comparisons showed weaker associations, suggesting some role for shared familial or genetic factors in the risk.

### Clinical Implications:

• **Modest but Clinically Relevant Risk:** The study highlights that MC is associated with a modest yet significant long-term increase in VTE risk. This is particularly important given the older age and comorbidity-prone nature of the MC population.
• **Heightened Clinical Awareness:** Healthcare providers should be aware of the increased VTE risk in patients with MC, especially in those with more severe disease or who require budesonide treatment.
• **Risk Assessment:** Routine risk assessment for VTE may be warranted in this population, particularly for those with additional risk factors such as immobility, obesity, or a history of thrombosis.

### Conclusion:

This study provides strong evidence that microscopic colitis is associated with a modest increase in long-term VTE risk. Given the potential complications of VTE, clinicians should consider proactive risk management strategies and maintain a high index of suspicion for thrombotic events in patients with MC.