Porphyria Cutanea Tarda

Overview – Porphyria Cutanea Tarda

Porphyria cutanea tarda (PCT) is the most common type of porphyria and results from a deficiency or inhibition of the hepatic enzyme uroporphyrinogen decarboxylase. This leads to accumulation of porphyrin intermediates, which are photosensitive and cause characteristic skin fragility, blistering, and pigmentary changes, especially in sun-exposed areas. PCT is highly relevant to final-year medical students due to its strong association with liver disease, iron overload, and hepatitis C.

Aetiology

  • Defect in uroporphyrinogen decarboxylase (UROD) enzyme
  • Hereditary in ~30% of cases
  • Acquired causes:

Pathophysiology

  • Deficiency of UROD disrupts the porphyrin-haem synthesis pathway
  • Results in accumulation of porphyrin intermediates in skin and urine
  • These compounds are photosensitising → Skin damage upon sun exposure

Clinical Features

  • Photosensitivity
  • Skin fragility and erosions on the dorsum of hands and forearms
  • Blisters containing clear or haemorrhagic fluid
  • Delayed healing with crusted erosions
  • Hyperpigmentation, milia, and post-inflammatory scarring
  • Involvement of other sun-exposed areas (e.g. scalp, face, neck)
  • Red-brown or “tea-coloured” urine (especially after sun exposure)
PORPHYRIA CUTANEA Tarda
Creative Commons Attribution 4.0 International License: https://www.ncbi.nlm.nih.gov/books/NBK537352/figure/article-27442.image.f1/

Investigations (Optional)

  • Raised plasma and urine porphyrins
  • Genetic testing for familial UROD mutations
  • Liver function tests, hepatitis screen, ferritin
PORPHYRIA CUTANEA Tarda
Change in urine colour before and after sun exposure Left figure is urine of the first day. Right figure is urine after sun exposure for 3 days. Urine colour changed to “port wine” colour after sun exposure. This colour change is due to increased concentrations of porphyrin intermediates in the urine, indicating an abnormality in production and a partial block within the enzymatic porphyrin chain with metabolite formation. The urine colour usually becomes darker with acute illness, even dark reddish or brown after sun exposure.
Chen GL, Yang DH, Wu JY, Kuo CW, Hsu WH, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons

Management

  • Avoid triggers:
    • Cease alcohol
    • Discontinue oestrogen (e.g. HRT)
    • Avoid excess iron (e.g. supplements, iron-rich diet)
  • Sun protection:
    • Protective clothing
    • Sunscreen (though often less effective than covering skin)
  • Treat underlying causes:
  • Iron reduction therapy:
    • Regular venesection (~500 mL every 2–4 weeks) until ferritin normalises
  • Hydroxychloroquine:
    • Promotes urinary excretion of porphyrins
    • Useful in patients unsuitable for venesection (e.g. elderly or anaemic)

Summary – Porphyria Cutanea Tarda

Porphyria cutanea tarda is a photosensitive blistering disorder caused by a defect in uroporphyrinogen decarboxylase. It presents with fragile skin, blistering, and pigmentary changes on sun-exposed areas, and often features dark urine. Management includes sun avoidance, treating underlying liver disease, and iron reduction. For related topics, see our Skin & Dermatology Overview page.

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