Porphyria is a group of disorders caused by defects in the haem synthesis pathway, leading to a build-up of porphyrins or their precursors. They are broadly divided into:
- Acute porphyrias, which mainly cause neurovisceral symptoms
- Cutaneous porphyrias, which mainly cause photosensitivity and skin problems
Two key types to remember are:
- Acute intermittent porphyria (the most common acute porphyria)
- Porphyria cutanea tarda (the most common overall)
Porphyrias are often inherited, although some forms (e.g., porphyria cutanea tarda) may be acquired or have non-genetic contributing factors.
Acute attacks are often triggered by:
- Medications (e.g., rifampicin, carbamazepine and oral contraceptives)
- Alcohol
- Fasting
- Infection
- Smoking
- Stress
- Hormonal changes during the menstrual cycle
TOM TIP: In your exam, look out for a patient with severe recurrent abdominal pain, psychiatric symptoms, peripheral neuropathy or dark/reddish urine, particularly after taking a triggering medication or during fasting. The underlying diagnosis might be acute intermittent porphyria. Alternatively, a patient with photosensitive blistering skin lesions may have a cutaneous porphyria.
Pathophysiology
Porphyria results from a deficiency of one of the enzymes involved in haem biosynthesis. This causes accumulation of haem precursors or porphyrins.
In the acute porphyrias, build-up of precursors such as aminolevulinic acid and porphobilinogen causes attacks of abdominal, neurological and psychiatric symptoms. In the cutaneous porphyrias, accumulated porphyrins in the skin react to light exposure, causing photosensitivity and skin damage.
Presentation
Acute porphyria may present with:
- Severe abdominal pain
- Vomiting or constipation
- Peripheral neuropathy
- Psychiatric symptoms, such as anxiety, agitation or confusion
- Tachycardia
- Dark or reddish urine (characteristically darkens on standing and exposure to light and air)
Cutaneous porphyria may present with:
- Photosensitivity
- Fragile skin
- Blistering lesions on sun-exposed areas
- Hyperpigmentation or scarring
Diagnosis
Diagnosis depends on the type of porphyria.
Urinary porphobilinogen (PBG) is the key test during acute attacks.
Cutaneous forms may require porphyrin testing in blood, urine or stool, depending on the suspected subtype.
Management
Patients should usually be managed with specialist input. Management depends on the subtype. Drug safety is particularly important in porphyria.
For acute porphyria:
- Avoid triggers where possible
- Stop unsafe medications
- High carbohydrate intake or IV glucose
- IV haem arginate if severe
For cutaneous porphyria:
- Sun protection
- Avoid precipitating factors
Last updated April 2026
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