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Porphyria

Porphyrias are inherited disorders of haem synthesis resulting in the accumulation of porphyrin and porphyrin precursors

There are 7 main types of porphyria; only 3 are considered here. 

  • Acute intermittent porphyria
    • Caused by a defect of porphobilinogen deaminase 
    • Most common in those around the age of 30
    • Females > males 5:1
    • Autosomal dominant inheritance, although only 10 to 20% of carriers become symptomatic 
    • Signs/symptoms may include
      • Abdominal pain
      • Tachycardia
      • Muscle weakness
      • Sensory changes in a ‘bathing suit’ distribution
      • Constipation
      • Nausea and vomiting
      • Postural hypotension
      • Hypertension
      • Low sodium 
      • Seizures 
      • Paralysis
      • Psychosis
    • Precipitants 
      • Medications – sulphonamides, methyldopa, danazol, diazepam, phenytoin, carbamazepine, sulphonylureas, chloramphenicol, tetracyclines, some anthistamines
      • Alcohol 
      • Illicit drugs – cocaine, amphetamines, ecstasy, marijuana
      • Fasting
      • Stress
      • Infections 
      • Smoking 
      • Pregnancy
      • Pre-menstrual hormone variation
    • Diagnosis
      • Urine dark on standing due to polymerisation of porphobilinogen to porphyrins 
      • Urinalysis of urine protected from light looking for raised aminolaevulinic acid and porphobilinogen
    • Management of acute attacks
      • Pain relief – opiates if required
      • Convulsions managed with gabapentin or vigabatrin
      • Monitor sodium – if low, fluid restrict 
      • Glucose 
      • Haem arginate - slow IV infusion 

  • Variegate porphyria 
    • Causesd by a mutation in the gene for protoporphyrinogen oxidase 
    • Most common in South Africans 
    • Features 
      • Cutaneous manifestations 
        • Photosensitive blistering
        • Hyperpigmentation
      • Abdominal pain
      • Dark urine 
      • Neuropsychiatric symptoms 

  • Porphyria Cutanea Tarda 
    • This is the commonest of all the porphyrias 
    • 2 forms – sporadic (around 90%) and familial (10%)
    • It is caused by a mutation in the gene encoding uroporphyrinogen decarboxylase 
    • Features
      • Light-sensitive dermatitis – blisters 
      • Hypertrichosis
      • Often iron overload 
      • Urine glows pink under Wood’s lamp due to raised uroporphyrinogen
    • Precipitants of attacks include 
      • Alcohol 
      • Iron 
      • Oestrogens 
      • Sunlight
    • Associations
    • Treatment: 
      • Avoidance of sunlight
      • Oral chloroquine
      • Venesection

References
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Abdelghafour

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