1194 Small Intestinal Bacterial Overgrowth Is Common in Mast Cell Activation Syndrome : Official journal of the American College of Gastroenterology | ACG

Secondary Logo

Journal Logo


1194 Small Intestinal Bacterial Overgrowth Is Common in Mast Cell Activation Syndrome

Weinstock, Leonard B. MD, FACG1; Brook, Jill MA2; Kaleem, Zahid MD3; Afrin, Lawrence MD4; Molderings, Gerhart MD5

Author Information
The American Journal of Gastroenterology 114():p S671, October 2019. | DOI: 10.14309/01.ajg.0000594304.61014.c5
  • Free



Mast cell activation syndrome (MCAS) often presents with symptoms of irritable bowel syndrome (IBS). MCAS is a multi-systemic disorder caused by inappropriate mast cell (MC) activation causing inflammatory and allergic symptoms. IBS can be associated with small intestinal bacterial overgrowth (SIBO). This study determined the prevalence of SIBO in MCAS.


Patients with refractory gastrointestinal (GI) symptoms were evaluated for MCAS and SIBO. MCAS was diagnosed if there were typical symptoms of mast cell (MC) activation in 2 or more organ systems plus 1 or more of the following: elevation of MC chemical mediator(s), clinical improvement with MC-directed therapy, and/or increased intestinal MC density. SIBO diagnosis was based on a lactulose breath test (LBT) with ≥20 ppm hydrogen rise from baseline within 90 minutes. These LBT results were compared to our prior study of healthy controls. The effect of co-morbid syndromes and medication use was analyzed. Antibiotic therapy effects were a secondary aim. This study was IRB approved.


There were 139 MCAS subjects (116 F, 23 M, 46.6 ± 16.9 years) and 30 controls (19 F, 11 M, 44 ± 14.0 years). GI symptoms preceded other MCAS symptoms in 66.2%. Symptoms included abdominal pain (87.1%), bloating (74.8%), constipation (66.9%), diarrhea (63.3%), nausea (61.9%), heartburn (54.0%), and dysphagia (29.5%). In these MCAS patients Rome 4 criteria for IBS-mixed (39.6%), IBS-constipation (22.3%), and IBS-diarrhea (18.7%) were met. SIBO was present in 30.9% MCAS subjects vs. 10% in controls (P = 0.023). Methane excretion in a plateau pattern was common in MCAS: 10.1% had levels ≥10 ppm and 24.5% had levels 3-9 ppm. Higher methane levels were associated with IBS-constipation compared to SIBO positive subjects: 42.9% vs. 9.3% (P = 0.02). Postural orthostatic tachycardia syndrome, hypermobile Ehlers-Danlos syndrome, MC density and mediators, proton pump inhibitors, thyroid supplements, and statins were not associated with LBT changes. Antibiotics were prescribed for 74 subjects: 67.6% had marked improvement, 5.4% had partial improvement, and 21.6% had no improvement in GI symptoms. Adverse events led to cessation of antibiotics in 9.5%.


SIBO with hydrogen and methane plateau patterns are common in MCAS subjects. MCAS could cause SIBO due to alterations of the GI immune system or altered motility by local release of MC mediators. Antibiotic therapy appears to improve GI symptoms in MCAS patients.

© 2019 by The American College of Gastroenterology