Acute intermittent porphyria: abdominal pain, weight loss and acute neuropathy

Acute intermittent porphyria (AIP) is an inherited neurovisceral metabolic disorder caused by impaired haem biosynthesis. A young woman developed recurrent abdominal pain, vomiting, constipation, weight loss, progressive weakness and hyponatraemia. Initial diagnoses included gastroenteritis, small intestinal bacterial overgrowth and avoidant restrictive food intake disorder. Neurophysiology identified a severe length-dependent, predominantly motor axonal polyneuropathy. Her weakness progressed despite nutritional support, vitamin replacement and intravenous immunoglobulin. Urinary porphobilinogen, delta aminolaevulinic acid and total porphyrins were markedly elevated, and genetic testing confirmed a likely pathogenic hydroxymethylbilane synthase variant, establishing AIP. Treatment with haem arginate rapidly improved her abdominal pain, arrested neurological progression and led to gradual functional recovery. This case highlights the diagnostic challenge of recognising AIP when there are credible alternatives and underlines caloric deprivation as both a precipitant and a confounder in neurovisceral presentations.