ICU · neurocritical-care

Acute Intermittent Porphyria — Comprehensive ICU Management

Also known as Acute intermittent porphyria · AIP · Acute porphyria · Porphobilinogen deaminase deficiency · HMBS deficiency · Acute neurovisceral porphyria · Port wine urine · Haem arginate

Acute intermittent porphyria (AIP) — autosomal dominant defect in porphobilinogen deaminase (PBGD/HMBS enzyme) in the haem biosynthesis pathway → accumulation of porphyrin precursors (ALA — aminolaevulinic acid, PBG — porphobilinogen) → neurotoxicity. Classic triad: ABDOMINAL PAIN (severe, persistent, out of proportion to examination — no peritonism) + NEUROLOGICAL symptoms (peripheral neuropathy, motor weakness, bulbar palsy, seizures) + PSYCHIATRIC symptoms (anxiety, hallucinations, paranoia). Urine turns DARK (port-wine/dark red) on standing or exposure to light (from porphobilinogen oxidation). Diagnosis: ELEVATED urinary porphobilinogen (PBG) and ALA (aminolaevulinic acid) — random spot urine (significantly elevated — over five times normal). Treatment: (1) IV HAEM ARGINATE 3 mg/kg once daily for 4 days (or haemin 3-4 mg/kg — reconstituted with human albumin — suppresses ALA synthase → reduces porphyrin precursor production), (2) CARBOHYDRATE LOADING (IV glucose for mild attacks only, or until haem is available — glucose in water solutions aggravate hyponatraemia), (3) STOP ALL PRECIPITATING DRUGS (barbiturates, sulfonamides, OCP, griseofulvin, rifampicin, phenytoin, carbamazepine, alcohol — check EVERY drug against the safe drug list), (4) SYMPTOMATIC: opiate analgesia (morphine/fentanyl — SAFE), antiemetics (ondansetron — SAFE; AVOID metoclopramide, phenothiazines), beta-blocker for tachycardia/hypertension (propranolol/labetalol — SAFE), levetiracetam for seizures (SAFE — AVOID barbiturates/phenytoin/valproate). ICU admission for: respiratory muscle weakness (motor neuropathy → ventilatory failure — like GBS), severe hyponatraemia (SIADH — common in acute porphyria), seizures, autonomic instability. Prognosis: acute attack resolves over days-weeks with treatment. Mortality 5-10% (from respiratory failure, seizures, arrhythmia).