ACE inhibitor-induced isolated intestinal angioedema mimicking functional bowel disorder: a case report

Angiotensin-converting enzyme (ACE) inhibitor-induced intestinal angioedema is a rare but clinically significant adverse drug reaction. Isolated visceral involvement, occurring without the cutaneous, oropharyngeal, or laryngeal manifestations classically associated with ACE inhibitor angioedema, is particularly under-recognised and is repeatedly mistaken for common gastrointestinal disorders. Most reported cases describe symptom onset within hours to days of initiation; cases with subacute onset over several weeks-mimicking a functional bowel disorder-are far less well characterised.

A 54-year-old Indian woman with essential hypertension developed recurrent diffuse abdominal pain, intermittent loose stools, and nausea approximately six weeks after starting enalapril 10 mg once daily. She had no urticaria, pruritus, facial swelling, or oropharyngeal involvement. Vital signs were stable, and abdominal examination demonstrated mild diffuse tenderness without peritoneal signs. She was managed at peripheral facilities for presumed acute gastroenteritis and subsequently irritable bowel syndrome, with no meaningful response to standard therapy. Comprehensive evaluation excluded infectious, inflammatory, autoimmune, and hereditary causes; serum complement C4 was normal. The clinical diagnosis of ACE inhibitor-induced isolated intestinal angioedema was made on the basis of (i) angioedema-type presentation in the absence of urticaria or pruritus, (ii) temporal association with enalapril, (iii) exclusion of alternative aetiologies, and (iv) complete resolution following drug withdrawal. Causality was assessed as "probable" by the Naranjo Adverse Drug Reaction Probability Scale (score 7) and by the WHO-UMC criteria. After a structured wash-out, the patient was transitioned to losartan, with sustained blood pressure control and no recurrence over three months of follow-up.

ACE inhibitor-induced angioedema can present as isolated intestinal involvement and may evolve over weeks rather than hours, closely mimicking a functional bowel disorder. A meticulous medication history, formal causality assessment, and an empirical drug-withdrawal trial should be considered in any patient with unexplained, treatment-refractory gastrointestinal symptoms taking an ACE inhibitor.