Acute Intermittent Porphyria

Key points

• Acute intermittent porphyria (AIP): a rare autosomal dominant defect in porphobilinogen (PBG) deaminase in haem synthesis, causing accumulation of ALA and PBG.
• Intermittent attacks: severe abdominal pain and vomiting, motor/autonomic neuropathy (hypertension, tachycardia) and psychiatric symptoms; commoner in women; precipitated by drugs, alcohol, fasting, infection and hormonal changes.
• Diagnosis: raised urinary porphobilinogen and ALA during an attack; urine may darken (red/brown) on standing or light exposure.
• Acute attack: remove precipitants; IV haem arginate (haematin) and a high carbohydrate/glucose load suppress the pathway; supportive care (fluids, analgesia, seizure control with safe drugs).
• Avoid precipitant drugs (barbiturates, sulphonamides, many anticonvulsants, oestrogens, alcohol). Skin is NOT photosensitive in AIP (unlike some other porphyrias).