S3193 When Eosinophils Excite: Impact of Increasing Rates of Diagnoses of Mast Cell Activation Syndrome on Subsequent Detection of Eosinophilic Gastroenteritis: A Retrospective Review

Introduction: Mast cell activation syndrome (MCAS) has seen a notable increase in diagnostic frequency over the past decade, possibly due to improved clinical awareness and broader diagnostic criteria. Concurrently, eosinophilic gastrointestinal disorders (EGIDs), particularly eosinophilic gastroenteritis (EGE), are being recognized with increasing prevalence. Given overlapping symptomatology and proposed immunologic connections, we aimed to evaluate whether rising MCAS diagnoses are associated with increased identification of EGE. Methods: A retrospective review was conducted using data from 3 tertiary academic medical centers from 2015-2023. ICD-10 codes for MCAS and EGE were used to identify adult patients (≥18 years). Charts were reviewed for temporal relationship of diagnoses, symptom profiles, endoscopic, and histologic findings. Incidence trends were analyzed, and logistic regression was used to assess the odds of EGE diagnosis following MCAS compared to matched controls without MCAS. Results: Of 68 patients diagnosed with MCAS, 6 (8.8%) were subsequently diagnosed with EGE within a median of 14.6 months. In comparison, among 68 matched controls without MCAS, only 1.63 (2.4%) were diagnosed with EGE (P < 0.001). Patients with MCAS had 3.8 times higher odds of developing EGE (odds ratio 3.81; 95% confidence interval 2.93-4.95). Common symptoms leading to EGE workup included persistent abdominal pain, diarrhea, and food intolerance. Histologic review showed elevated mucosal eosinophil counts (>30 eos/hpf) predominantly in the small bowel. No significant differences in EGE severity or treatment response were noted between groups. Conclusion: This study suggests a strong association between a prior diagnosis of MCAS and subsequent identification of EGE. While the relationship may reflect heightened clinical vigilance and overlapping symptom profiles, shared pathophysiologic mechanisms involving immune dysregulation may also contribute. Further prospective studies are needed to elucidate causality and inform optimal screening strategies in MCAS patients.