Clinical Case Summary

A 54-year-old male with no significant past medical history presented with a five-year history of chronic gastrointestinal and systemic symptoms. He was initially diagnosed with irritable bowel syndrome (IBS) based on recurrent postprandial bloating, periumbilical abdominal discomfort, alternating diarrhea and constipation, and a persistent sensation of gastric fullness independent of food intake. Despite comprehensive management and a low-FODMAP diet, he reported minimal to no clinical improvement.
In addition to gastrointestinal complaints, the patient described recurrent headaches and chronic fatigue, both temporally associated with the consumption of histamine-rich foods such as red wine, aged cheeses, and processed meats. The neurological evaluation was unremarkable. Laboratory investigations were within normal limits, including complete blood count, inflammatory markers, liver and renal function tests, and celiac serologies. Gastroscopy and colonoscopy excluded structural, neoplastic, and inflammatory gastrointestinal pathology. However, serum diamine oxidase (DAO) activity was significantly decreased (2.8 U/mL; reference >10 U/mL), suggesting histamine intolerance secondary to DAO deficiency as the underlying etiology.
Therapeutic intervention included a strict low-histamine diet, oral DAO supplementation, and intermittent use of H1-antihistamines for symptomatic exacerbations. At a three-month follow-up, the patient reported substantial improvement in gastrointestinal and systemic symptoms, including normalizing bowel habits, resolution of headaches, and alleviating fatigue and bloating.
This case underscores the importance of considering histamine intolerance in patients with persistent IBS-like symptoms, particularly when conventional therapeutic strategies fail and symptom patterns suggest dietary histamine sensitivity. DAO activity testing may aid in diagnosis and guide effective, targeted therapy.

Disclosure

No Conflict of Interest.