MCAS patients suffer a variety of GI ailments, which are largely in common with SM.
Aerophagia, excessive swallowing of air, is very common. It is not entirely obvious why this occurs. In other patient populations, aerophagia is usually due to poor coordination between swallowing and respiration. Severe cases can lead to abdominal distention, aspiration of stomach contents into the lungs and esophageal rupture.
Chest discomfort is common in MCAS. Cardiac issues should be ruled out, but in most people, it is due to esophagitis. Some patients have a previous diagnosis of reflux but it is refractory to all relevant treatments.
Diarrhea and constipation, sometimes alternative, are very common. In one study, 89% of MCAS patients studied had frequent nausea, 100% had abdominal pain of some nature, and 69% had noncardiac chest pain. Partial bowel obstructions are uncommon, but do occur in MCAS. They are thought to be due to focal dysmotility or focal edema.
IBS is a frequent previous diagnosis in MCAS. The GI tract often looks normal by eye and typical H&E staining shows mild inflammation. Staining for mast cells often shows they are increased. Of note, there is not a universal consensus on what is considered “increased mast cells” in GI samples. Generally, above 20 cells per hpf is marked as high by pathologists. Presence of the D816V CKIT mutation is rare in GI biopsies of MCAS patients.
Selective malabsorption of certain nutrients is often seen in MCAS. Iron malabsorption is by far the most common. Copper and B vitamins are often poorly absorbed as well. Protein calorie malabsorption is rare, but leads to weight loss and wasting.
Pancreatic enzyme supplementation can be helpful in treatment of diarrhea, weight loss and malabsorption. The fact that this often works suggests that MCAS driven inflammation or fibrosis causes pancreatic exocrine deficiency, a condition in which the pancreas does not make enough digestive enzymes. Mast cells have a known link to painful chronic pancreatitis. In patients with painful vs painless chronic pancreatitis, mast cell density is 3.5X higher in pancreas biopsy.
About half of MCAS patients have some kind of liver abnormality. Fibrosis (obliterative portal venopathy) is the most common. However, fatty metamorphosis, sinusoidal dilatation, venoocclusive dilatation, nodular regenerative hyperplasia and cirrhosis have also been seen. Sterile (non-infectious) inflammation of the liver and portal trial infiltration by lymphocytes and eosinophils has also been identified in a number of patients. In particular, these patients often have a 2-3X elevation in transaminases and/or alkaline phosphatase, determinants of liver function. Impeded flow of bile from the liver is usually absent. Portal hypertension is unusual but has occurred, causing swelling of the spleen and varices in the esophagus. Rarely, free fluid in the abdomen (ascites) has occurred in MCAS patients.
One study found that 75% of MCAS patients tested had high cholesterol levels. Importantly, 79% of patients had “normal” BMI or were underweight, so the high cholesterol was not correlated to weight. 44% had a twofold or greater elevation of liver enzymes. 36% had increased bilirubin in the blood. 15% had fatty liver; 13% had swelling of the liver; 4% had cysts; 4% had adenomas; 2% had hemangiomas. 14% of patients had pancreatic involvement with elevated lipase or amylase.
Kirsten Alfter, Ivar von Ku gelgen, Britta Haenisch, Thomas Frieling, Alexandra Hu lsdonk, Ulrike Haars, Arndt Rolfs, Gerhard Noe, Ulrich W. Kolck, Jurgen Homann and Gerhard J. Molderings. New aspects of liver abnormalities as part of the systemic mast cell activation syndrome. 2009 Liver International 29(2): 181-186.
Afrin, Lawrence B. Presentation, diagnosis and management of mast cell activation syndrome. 2011. Mast Cells.