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
- Hepatitis C
- Haemochromatosis
- Treatment:
- Avoidance of sunlight
- Oral chloroquine
- Venesection
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