Porphyria

Inherited disorders of haem synthesis.

Acute and non-acute

Acute
  • Acute Intermittent Porphyria (AIP)
  • Variegate Porphyria (VP)
  • Hereditary Coproporphyria (HCP)
All are enzyme deficiencies in the haem synthesis pathway and result in the accumulation of ALA.
Either accumulation of ALA or deficiency of haem result in neurovisceral crises - neurological dysfunction in motor, sensory, autonomic fibres and CNS

Precipitants:
  • Drugs
  • Fasting
  • Dehydration
  • Infection
  • Stress
  • Alcohol
Crises more common in women

Symptoms and signs
  • Abdominal pain
  • Tachycardia
  • Hypertension
  • Weakness (20% develop respiratory failure, bulbar palsy if severe) - differential diagnoses are GB, polio and lead poisoning
  • Delerium, psychosis
  • Seizures
  • Automonic - ileus, postural hypotension
  • Cutaneous lesions
  • Hyponatraemia

Most present with severe abdominal pain and tachycardia


Diagnosis
Test urine for porphobilinogens (sample must be protected from light)

Treatment

  • Remove precipitants
  • IV heam arginate 3mg/kg for 4 days (replenishes haem so reduces synthesis)
  • Carbohydrate - need 200g of glucose / day
  • Supportive - pain control, ventilation, haloperidol for delerium, B-blockers or clonidine for tachycardia and hypotension, seizure control (many antiepileptics precipitate porphyria so check - benzos, levetiracetam and gabapentin ok). Propofol, alfentanil, clonidine, LMWH and ranitidine all safe.

See CEACCP article for more info