according to an American Gastroenterological Association clinical practice update.
Although the allergic response is best known for a combination of anaphylaxis, skin changes, and gastrointestinal symptoms that occurs within hours of consuming mammalian-derived food products, health care providers should know that many patients experience gastrointestinal distress in the absence of other clinical signs, lead author Sarah K. McGill, MD, MSc, of the University of North Carolina at Chapel Hill, and colleagues reported.
Dr. Sarah McGill
“It is important for gastroenterologists to be aware of this condition and to be capable of diagnosing and treating it in a timely manner,” the investigators wrote in Clinical Gastroenterology and Hepatology.
To this end, Dr. McGill and colleagues drafted the present clinical practice update, covering pathogenesis, clinical manifestations, diagnosis, and management.
“The allergy in alpha-gal syndrome is to galactose alpha-1,3-galactose, an oligosaccharide on the cells of all nonprimate mammals,” the investigators wrote. “Surprisingly, sensitization to alpha-gal, that is, the process by which human beings develop IgE antibodies to the sugar, is understood to occur after the bite of a tick or parasitic infection. In the United States, the Lone Star tick, an ectoparasite whose principal host is deer, is strongly implicated.”
Gastrointestinal focused clinical research is scarce, the investigators noted, citing two observational studies involving 375 patients positive for alpha-gal IgE. Almost half of these patients (40.7%) had gastrointestinal symptoms alone. Across the entire population, the most common gastrointestinal symptoms were abdominal pain (71%) and vomiting (22%). About three out of four patients reported improvement on an alpha-gal avoidance diet.
“Clinicians should consider alpha-gal syndrome in the differential diagnosis of patients with unexplained gastrointestinal symptoms of abdominal pain, diarrhea, nausea, and vomiting, particularly those who live or have lived in an alpha-gal–prevalent area,” the investigators wrote.
In the United States, these areas span the domain of the Lone Star tick, including most of the East Coast, the central Midwest, the South, and all of Texas. Overseas, alpha-gal syndrome has been reported in Japan, Australia, Western Europe, and South Africa.
Clinical suspicion should be increased in patients with a history of tick bite, engagement in outdoor activities, and awakening in the night with gastrointestinal distress (because of the delay between allergen ingestion and symptom onset). Workup should include serum testing for alpha-gal IgE antibodies, according to the update. Serum positivity alone, however, is not sufficient for diagnosis. Alpha-gal syndrome must be confirmed by symptom resolution or improvement upon adherence to an alpha-gal avoidance diet for at least a month.
“During this time, patients may want to avoid eating at restaurants, which can easily cross-contaminate food, and processed food, which may contain alpha-gal in additives,” Dr. McGill and colleagues wrote.
Patients with alpha-gal syndrome who accidentally consume alpha-gal should take 25-50 mg of diphenhydramine and ensure access to a self-injectable epinephrine if symptoms progress, particularly if respiratory compromise occurs, they added.
The coauthors are Jana G. Hasash, MD, and Thomas A. Platts-Mills, MD, PhD.
The investigators disclosed relationships with Olympus America, Exact Sciences, Guardant Health, Finch Therapeutics, and others.