Acute intermittent porphyria

Background

• Acute Intermittent Porphyria is a disorder caused by the inability to produce heme, a component of hemoglobin in red blood cells.
• The defective enzyme is porphobilinogen deaminase.
• Patients typically present with dark urine, abdominal pain, and psychiatric disturbances

Triggers

• Infection
• Metabolic stress and starvation
• ETOH
• CYP450 Inducers: sulfonamides, barbiturates, rifampin or metoclopramide

Clinical Features

• Gastrointestinal symptoms
  • Acute abdominal pain (85-90% of attacks)
  • Port wine-colored urine
  • Agitation, confusion, combativeness, seizure

Differential Diagnosis

Extra-abdominal Sources of Abdominal pain

• MI
• Aortic Dissection
• PNA
• PE
• Testicular Torsion
• Herpes Zoster
• Muscle spasm
• Spinal pathology
• Strep Pharyngitis (peds)
• Mononucleosis
• DKA
• ETOH Ketoacidosis
• Uremia
• Sickle Cell Crisis
• SLE
• Vasculitis
• Glaucoma
• Hyperthyroidism
• Methanol Poisoning
• Heavy Metal toxicity
• Addison's disease
• Porphyria
  • Acute intermittent porphyria
• Paroxysmal nocturnal hemoglobinuria
• Black widow spider bite

Evaluation

Consider porphyria in patients with abdominal pain that is unexplained after an initial workup has excluded common causes (appendicitis, cholecystitis, pancreatitis, etc).

• Spot urinary porphobilinogen (sendout at most hospitals)
  • Normal = 0-4mg/day
  • acute attack, spot urine can be 20-200mg/L
• Recurrent attacks in a patient with proven acute porphyria are usually similar and can be diagnosed on clinical grounds without biochemical reconfirmation.

Management

• Goal to decrease heme synthesis and reduce production of porphyrin precursors
• High doses of glucose, e.g. D5NS at 2L/hr x 24h
  • Avoid D5W or D10W as may aggravate hyponatremia
• Severe attacks, especially with severe neuro symptoms: hematin 4mg/kg/d x 4d

See Also

• Abdominal pain
• Porphyria

Video

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