Updated: 3/12/2017

Acute Intermittent Porphyria

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  • A 32-year-old woman presents to the psychiatric emergency room for uncooperative behavior and hysteria. She complains of abdominal pain. While being evaluated, she had a generalized tonic-tonic seizure. She has no family or personal history of seizures. Her serum studies ruled out any metabolic abnormalities that may cause seizures. Neurologic exam showed extensive peripheral neuropathy. Urine showed high titers of porphobilinogen.
Introduction

  • Clinical definition
    • acute intermittent porphyria (AIP) is an inherited metabolic disease resulting from deficiency in the heme synthesis pathway porphobilinogen deaminase (PBD)
  • Epidemiology
    • incidence
      • AIP is the most common type of acute porphyria but still relatively rare
      • 0.13 per year per million persons
    • demographics
      • women > men
      • 20-40 years of age
    • risk factors
      • female gender
  • Pathophysiology
    • pathobiology
      • deficiency of porphobilinogen deaminase (step 3 in heme pathway, see illustration)
      • attacks are precipitated by an exposure
        • exposure increases demand of the heme pathway
          • resulting in an accumulation of intermediates, aminolevulinic acid (ALA) and porphobilinogen (PBG) which are both neurotoxic
        • precipitating factors
          • most commonly drugs
            • cytochrome P-450 inducers
            • anticonvulsants
            • oral contraceptive pills
          • smoking
          • infection
          • starvation
          • fluctuating hormones (menstrual cycle in women)
  • Genetics
    • inheritance pattern
      • autosomal dominant
    • mutations
      • HMBS (aka PBGD), encoding PBD
  • Prognosis
    • most patients fully recover
    • < 5% have recurrence
Presentation
  • Symptoms
    • often nonspecific and vague
    • primary symptoms (5 P’s)
      • severe abdominal pain without tenderness on palpation
      • neurological symptoms
        • polyneuropathy
        • seizures, weakness, and paralysis
      • psychiatric symptoms
        • anxiety and insomnia
      • port wine-colored urine
      • precipitated by an exposure
    • vomiting
    • constipation
  • Physical exam
    • vitals
      • tachycardia
      • hypertension
    • neurologic signs in severe attacks
      • loss of tendon reflexes
      • motor stiffness/paralysis
    • the rest of physical exam is often normal
Imaging
  • Radiographs  
    • abdominal radiography
      • indication
        • often initially obtained due to nonspecific nature of symptoms
      • findings
        • normal
Studies
  • Labs
    • serum studies
      • may see hyponatremia
    • urine studies
      • ↑ PBG, aminolevulinic acid, and uroporphyrin III
    • stool studies
      • no fecal porphyrin
        • note, fecal porphyrin may be elevated in other types of porphyrias
Differential
  • Small bowel obstruction 
    • tenderness on palpation
  • Lead poisoning 
    • no elevated PBG in urine
Treatment
  • Remove precipitating factors
  • Medical
    • heme infusions
      • indication
        • for severe attacks
    • glucose
      • indications
        • for minor attacks
        • if heme is not available
      • requires close monitoring of serum sodium to exclude hyponatremia
Complications
  • chronic neuropathic pain
    • treatment
      • gabapentin
 

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