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Cutaneous porphyrias — porphyria cutanea tarda and protoporphyria
In cutaneous porphyrias, porphyrins accumulate in the skin and absorb blue-violet light (around 400–410 nm), causing damage in exposed areas; porphyria cutanea tarda (PCT) causes blisters and skin fragility on the backs of the hands, and protoporphyria causes immediate burning pain in sunlight without blisters.
Why it matters in the exam
The classic stem: a middle-aged man with blisters, erosions, scars and milia on the backs of the hands, facial hypertrichosis and dark urine, with alcohol use, hepatitis C or oestrogen intake. Asked are the defective enzyme (UROD), the test (urinary porphyrins), the triggers (iron, alcohol, HCV, oestrogen, HIV, haemochromatosis) and the treatment: venesection or low-dose hydroxychloroquine. A child who cries in pain as soon as they go into the sun — protoporphyria. Remember also that acute porphyrias such as AIP cause no skin findings, and that variegate porphyria can combine PCT-like blisters with acute attacks. For the exam remember that a Wood lamp shows pink-red fluorescence of the urine in PCT, that porphyrins are classified by their location in urine, stool or red cells, and that visible-light protection is part of every treatment, including protective clothing, filtering glass and an opaque mineral sunscreen.
Key points
- In cutaneous porphyrias, porphyrins in the skin absorb blue-violet light around 400–410 nm and cause damage in exposed areas.
- PCT results from reduced hepatic UROD activity and presents with blisters, skin fragility, milia and facial hypertrichosis.
- PCT triggers include alcohol, iron, hepatitis C, oestrogen, HIV and HFE mutations.
- PCT is treated with venesection or low-dose hydroxychloroquine, together with treating the trigger and light protection.
- EPP appears in childhood with immediate burning pain in the sun without blisters and is diagnosed by raised red-cell protoporphyrin.
Summary table
| Disease | Enzyme and source | Clinical picture | Diagnosis and treatment |
|---|---|---|---|
| Porphyria cutanea tarda (PCT) | Reduced hepatic UROD activity | Blisters, skin fragility, milia and scars on the backs of the hands, facial hypertrichosis | Raised urinary uroporphyrin; venesection or low-dose hydroxychloroquine; treat HCV |
| Erythropoietic protoporphyria (EPP) | Ferrochelatase deficiency, bone-marrow source | Immediate burning pain on sun exposure, swelling, no blisters, from childhood | Raised red-cell protoporphyrin; afamelanotide; risk of gallstones and liver disease |
| Variegate porphyria | PPOX deficiency | PCT-like blisters together with acute neurovisceral attacks | Faecal and plasma porphyrins; avoid triggering drugs |
| Pseudoporphyria | No enzyme deficiency | PCT-like blisters but normal porphyrins | Drugs: naproxen, tetracyclines, furosemide; dialysis; remove the cause |
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Sources
- British Porphyria Association and BAD guidance on porphyria cutanea tarda, 2020 — Diagnosis and treatment
- European Porphyria Network recommendations, 2021 — Erythropoietic protoporphyria
- Fitzpatrick's Dermatology, 9th edition (2019) — The porphyrias
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.