Recurrent self-limiting abdominal pain with bowel wall edema misdiagnosed as gastroenteritis: a case report of C1-inhibitor-deficient hereditary angioedema

Hereditary angioedema (HAE) due to C1 esterase inhibitor (C1-INH) deficiency is a rare bradykinin-mediated disease characterized by recurrent episodes of angioedema. Gastrointestinal manifestations can resemble an acute abdomen and are often misdiagnosed, contributing to delayed recognition. We describe a 35-year-old man with two previous self-limited episodes of abdominal pain with diarrhea over the preceding year, beginning in August 2024, each lasting approximately five days, both of which were diagnosed as acute gastroenteritis and treated with symptomatic intravenous therapy. He presented with acute paroxysmal right lower quadrant abdominal pain and watery diarrhea, without fever, nausea, or vomiting. Contrast-enhanced abdominal computed tomography revealed segmental ileal wall edema with ascites, showing slight progression on repeat imaging later the same day. Laboratory analysis demonstrated leukocytosis with neutrophilia and significantly elevated D-dimer levels. Complement testing showed a significantly reduced C4 concentration (0.08 g/L) and a normal C3 level (0.84 g/L), raising suspicion of HAE. Further evaluation confirmed profoundly decreased functional C1-INH activity (<7%) and a reduced C1-INH antigen level (18.89 μg/mL), establishing a diagnosis of type I HAE. The patient improved following supportive and antispasmodic treatment, and no HAE-specific bradykinin-targeted therapy was administered during this admission. This case emphasizes that recurrent, self-limited abdominal pain accompanied by imaging evidence of transient small-bowel wall edema and ascites should prompt consideration of abdominal HAE. Early assessment of complement C4 is a practical screening strategy that enables timely confirmatory testing and minimizes the likelihood of repeated misdiagnosis.