Acute intermittent porphyria

Definition

• Autosomal dominant mutation in HMB synthase with variable penetrance causing intermittent attacks characterized by neurovisceral symptoms

Etiology

• Defect in heme synthesis; specifically, in HMB synthase (hydroxymethylbilane synthase; porphobilinogen deaminase), which causes build-up of porphobilinogen

Clinical Presentation

History

• Prodromal symptoms, including restlessness
• Neurovisceral symptoms, including abdominal pain, tachycardia, constipation, psychosis, seizures, paralysis

Signs & Symptoms

• Red-brown urine

Investigations

• Electrolytes: may show hyponatremia or other abnormalities
• Urine porphyrins (PBG)

Management

Acute

• Stop offending medication, start high carb diet
• Sometimes hematin
• If seizures: gabapentin or levitiracetam

Chronic

• Avoid triggers, including drugs
• High-carb diet
• Screen for cirrhosis and hepatocellular carcinoma