S4483 Mast Cell Activation Syndrome: An Entity Overlapping With Irritable Bowel Syndrome and Often Ignored

Introduction: Mast cell activation syndrome (MCAS) displays diverse inflammatory and allergic symptoms across multiple body systems. Symptoms affecting the gastrointestinal (GI) tract include dyspepsia, gastroesophageal reflux, abdominal pain, nausea, vomiting, diarrhea, constipation, gastroparesis, angioedema, dysphagia (usually proximal), bloating (post-prandial or spontaneous), and malabsorption. Patients with MCAS exhibit a range of symptoms, including irritable bowel syndrome (IBS)-like symptoms, various dysautonomia types, neuropathy, myalgia, migraine, headache, cognitive dysfunction, restless legs syndrome, sleep disturbances, non-pulsatile tinnitus, depression, anxiety, and panic attacks. The general population is estimated to have a 17% prevalence. In gastroenterology, MCAS is prevalent yet frequently excluded from diagnostic considerations. Misinterpretations of non-GI symptoms as IBS are common due to the past overemphasis on IBS as a psychosomatic illness. Medical school curricula typically exclude MCAS. Due to unsatisfactory medical experiences, individuals with MCAS may consult many specialists but eventually stop reporting their symptoms. This office-based case series highlights the importance of differentiating MCAS and IBS patients. Case Description: Case series included 4 patients with suspected MCAs. Two underwent colonoscopy (1 White woman aged 36 years and 1 White man aged 49 years), and 2 underwent esophagogastroduodenoscopy (EGD) (1 Asian man age 39, and 1 White woman age 43). Colonoscopy biopsies were taken from the transverse colon, with 53 mast cells per high-powered field (MC hpf) and 60 MC hpf found for the woman and man, respectively. EGD biopsies taken from the stomach showed 20 MC hpf and 31 MC hpf for the man and woman, respectively. Immunohistochemical staining (CD117) revealed a range of 20-60 MC hpf. Follow-up biopsies to confirm histological response were not performed. Discussion: Patients previously diagnosed with IBS received a MCAS diagnosis based on complex histories, multi-organ symptoms, non-bloody diarrhea (no alarm symptoms), negative endoscopies, and GI tract biopsies revealing mast cell hyperplasia via special staining. The patients' response to histamine H1/H2 antagonists supported our MCAS diagnosis. This case series highlights that MCAS may be overlooked due to a limited understanding of GI symptom prevalence and characteristics. MCAS is neglected due to IBS' high prevalence (up to 40% in healthy individuals), overlapping symptoms with IBS, and overall unfamiliarity within the medical community. We propose that MCAS should be evaluated in patients with IBS symptoms. Testing for elevated serum tryptase can aid in diagnosing the active stage. Gastrointestinal mucosal biopsies with specialized staining for mast cells should be conducted in all suspected cases. The effectiveness of antihistamines and H2 receptor antagonists should be assessed in a therapeutic trial involving suspected cases.