ICU · Neurocritical Care

Acute intermittent porphyria (AIP)

Also known as Acute intermittent porphyria (AIP) · Porphyric crisis · Swedish porphyria · Hemin therapy

AIP is a rare autosomal dominant defect in hepatic haem biosynthesis caused by deficient porphobilinogen deaminase (hydroxymethylbilane synthase, HMBS). Presents with acute neurovisceral attacks triggered by drugs (barbiturates, sulfonamides, hormonal contraceptives, antiepileptics, alcohol), fasting, infection, surgery and stress. Classic triad: abdominal pain (severe, out of proportion to exam, with a benign abdomen) + neurological symptoms (motor neuropathy, seizures, psychiatric disturbance) + autonomic dysfunction (tachycardia, hypertension, constipation, urinary retention). Urine turns dark/red on light exposure. Diagnosis: markedly elevated urinary porphobilinogen (PBG) and aminolevulinic acid (ALA) on a random spot urine, confirmed by HMBS genetic testing. Treatment: withdraw all triggers, IV haem arginate 250 mg or 3 mg/kg once daily for four daily infusions (IV glucose alone only for mild attacks or until haem is available), opiate analgesia, phenothiazines/ondansetron for nausea, gabapentin/levetiracetam for seizures, and correct SIADH hyponatraemia. Ventilation may be needed for motor neuropathy.