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Porphyria cutanea tarda (PCT) is the most common type of porphyria.
An increase in porphyrins in the skin result in photosensitivity, ie, the skin is damaged by light.
Individuals with PCT present with increasingly fragile skin on the back of the hands and the forearms. Features include:
Although these features may also occur on the face and neck as well, it is more common to notice mottled brown patches around the eyes and increased facial hair (hypertrichosis). Occasionally the skin becomes hardened (scleroderma) on the neck, face or chest. There may be small areas of permanent baldness (alopecia) or ulcers.
Characteristically, the urine is darker than usual, with a reddish or tea-coloured hue.
The clinical appearance of variegate porphyria is similar but the biochemical abnormality is different.
PCT is due to a defective enzyme in the liver (uroporphyrinogen decarboxylase). This is involved in synthesis of the red pigment in blood cells (haem). Some families carry an enzyme that is prone to oxidation under certain circumstances, most often due to iron accumulation.
There are basically two forms of PCT, type 1 and type 2.
Type 1 PCT generally begins in mid-adult life after exposure to certain chemicals that increase the production of porphyrins (precursors of haem) in the liver. These include:
Type 2 PCT is familial and associated with abnormal genetic variants of uroporphyrinogen decarboxylase. Trigger factors are less often involved and onset of PCT is often younger than in type 1 PCT.
Other important tests include:
If a blood ferritin shows iron stores are increased, further investigations may include transferrin saturation and genotyping for hereditary haemochromatosis.
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