Porphyria

Background

• "Porphura" (Greek) = purple = urine colour during attack
• Rare, hereditary (very rarely acquired) haem synthesis errors (porphyrins)
• Acute or chronic
• F>M (rare before puberty & after menopause)
• Only 10% have recurrent attacks
• Check FHx

Clinical (acute episode)

Neuro, psychiatric, cuteneous, visceral

• Abdo pain (90%), usually colicky, ±diarrhoea, with soft abdomen
• Myalgia / weakness (proximal>distal, UL>LL)
• Autonomic dysfunction (sympathetic stimulation common)
• Psychosis or other psychiatric presentations
• Skin lesions (blistering) rare except in porphyria cutanea tarda
• Hyponatraemia (± seizures) due to SIADH in 40%
• Dark urine (on exposure to light)

Investigations

• Urine porphyrin studies (ask lab for collection details)
• High ALA and PBG (during attack) very sensitive and specific
• Stool porphyrin studies/ration (ask lab for details)
• Other (erythrocyte, genetic) tests if ALA/PBG tests positive

Management (acute)

• Analgesia
• Withdraw triggering drugs (Barbiturates, Anticonvulsants, Progestins, Rifampin)
• Give glucose (high carbohydrate intake). Start 10% dextrose infusion
• Actively manage hyponatraemia (& ↓Mg⁺⁺)
• ↟BP/↟HR respond to Β-blockers
• Haem arginate (donor IV haem) - ask haematology for advice
• Avoid sunlight if cuteneous
• PCT may later require phlebotomy to reduce liver iron stores

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