Porphyria cutanea tarda (PCT): symptoms, causes and treatment

The porphyrias are a group of disorders caused by enzyme defects in the biochemical pathway that makes haem, the component of blood that carries oxygen. BAD explains that these defects can result in a build-up of chemicals called porphyrins. In PCT the porphyrins are produced by the liver and travel to the skin, where they react to light.

The British Porphyria Association is a national charity for people with porphyria, offering patient information, leaflets and a helpline. The condition is uncommon, affecting about 1 in 25,000 people according to BAD.

There are two types. BAD says type 1, or sporadic PCT, is the commonest, accounting for 80 per cent of patients, and is not inherited. Type 2, or familial PCT, accounts for 20 per cent and is due to an inherited gene change. Not everyone who inherits the gene change develops the condition, because other factors need to be present.

According to BAD, the skin of sun-exposed areas is affected, particularly the very thin skin on the backs of the hands and sometimes the face and scalp. The symptoms develop gradually and the skin becomes unusually fragile.

• Blisters on sun-exposed skin that burst and heal slowly.

• Scars and tiny white raised spots called milia.

• Fragile skin, where even mild injury causes grazes and scars.

• Darkening of the skin colour and increased hair growth on the hands and face.

• Dark-coloured urine.

BAD lists the most common factors that bring on or worsen PCT: excessive alcohol consumption, oestrogen therapy including the combined contraceptive pill and hormone replacement therapy, viral infections of the liver such as hepatitis C, and iron accumulation in the liver. Nearly all patients have increased iron in the liver, which is believed to be partly responsible for the enzyme blockage, and some also have an inherited condition called haemochromatosis that causes the iron build-up.

This explains why investigation of PCT usually includes the liver and iron levels rather than the skin alone. It is rare for more than one family member to have PCT, but BAD says that if relatives have similar signs and symptoms they can be tested, while screening of relatives without skin problems is not generally required.

BAD says PCT is diagnosed by measuring porphyrins in samples of blood, urine and faeces. The samples need to be collected into special darkened containers that exclude light, for example by wrapping the specimen container in foil, so that light is excluded.

Other tests, such as liver function, glucose and iron levels, may be done to look for the associated conditions described above. Depending on the results you may be referred to another specialist, for example a liver doctor (hepatologist).

BAD says the underlying cause cannot be cured, but symptoms can be controlled. The first step is attention to exacerbating factors: avoiding sunlight, stopping the combined contraceptive pill and avoiding excess alcohol. Women on oestrogen treatments will be asked to stop them while PCT is being treated, though BAD says it may be possible to restart hormone treatment afterwards.

BAD says that while treatment takes effect the skin remains fragile and sensitive to bright sunlight. Conventional sunscreens are formulated mainly against UVB and may not be effective in PCT because the symptoms are triggered by UVA and visible light. Reflectant sunscreens based on titanium dioxide or zinc oxide are more effective because they cover UVA, UVB and visible light. BAD also mentions a tinted reflectant sunscreen available on prescription.

Avoiding excess alcohol is advised, and some people may need to abstain altogether. BAD also notes that people who avoid all sun exposure may become short of vitamin D and should consider having their level measured, and suggests that vitamin D3 and foods rich in vitamin D may be considered if levels are low.

PCT is usually diagnosed and managed by dermatology, with input from haematology or hepatology where needed. BAD notes that specialist UK porphyria services exist for the wider group of porphyrias. A GP can start the process by arranging blood tests and referring you.

Private dermatology or hepatology consultations are available to people who prefer them, and specialised porphyria tests need to be sent to a laboratory able to run them. Whoever you see, it helps to bring a list of your medicines, including hormonal contraception or HRT, and to be clear about your alcohol intake, as these are directly relevant to treatment.