Porphyria cutanea tarda (PCT) is the most common form of porphyria but is still rare, affecting only 1 in every 10,000 to 25,000 people in the general population. It usually develops after the age of 30 and can impact men and women of all ethnicities.
Contents of this article:
What is porphyria?
Porphyria causes photosensitivity, making it difficult to expose skin to sunlight without the risk of a reaction.
Porphyria is a rare group of blood conditions that occurs when the body does not have enough of certain enzymes to make heme.
Heme is a component of hemoglobin, the protein that transports oxygen around the body.
The body also needs heme to make several different proteins and is most commonly found in red blood cells, bone marrow, and the liver. In short, heme is a molecule vital for keeping the body's systems and organs functioning properly.
To make heme, the body uses enzymes to convert certain compounds into porphyrin. Different enzymes then convert this porphyrin into heme.
If this process breaks down, porphyrins build up in the body instead of being converted into heme, causing either acute attacks of pain or damage to the skin.
The type of porphyria a person has depends on which enzyme they lack.
Porphyrias that affect the brain are called acute porphyrias, and those that affect the skin are called cutaneous porphyrias.
Disorders that share the characteristics of both are called neurocutaneous porphyrias.
What causes porphyria cutanea tarda?
Photosensitivity can cause blisters and lesions on skin that has been exposed to sunlight.
Image credit: M Lecha, H Puy, JC Deybach, Orphanet J Rare Dis (2009).
PCT is a cutaneous porphyria caused by a deficiency of the enzyme uroporphyrinogen decarboxylase (UROD), which helps convert porphyrins into heme.
Symptoms usually occur when levels of UROD drop to around 20% of normal levels.
An accumulation of iron in the blood can also be a contributing factor. People with an iron overload disorder are at risk of developing PCT.
About 75-85 percent of people who have PCT acquire it rather than inherit it. PCT occurs when the body's ability to make UROD is interrupted.
PCT can be caused by hepatitis C, HIV, and excessive alcohol consumption. Some drugs containing estrogen, such as oral contraceptive pills or prostate cancer treatments, can also lead to a build-up of porphyrins in the blood, liver, and skin.
A minority of people with the condition have familial PCT, which means the UROD deficiency is genetic. However, most people with an inherited deficiency will never experience symptoms.
PCT causes photosensitivity, which is an extreme sensitivity to sunlight.
Photosensitivity can cause painful, blistering lesions on skin that has been exposed to the sun, usually on the hands and face. The skin in these areas can be particularly fragile, and may blister or peel if subjected to even minor trauma. The resulting lesions may crust over.
Over time, scarring may cause the skin to darken or fade. This is called hyperpigmentation or hypopigmentation.
Some people with PCT may also experience excessive, abnormal hair growth. This usually happens on the face, and the hair can be fine or coarse and differ in color. Some people may see their hair grow, thicken, and darken.
Milia, small bumps with white heads, can also develop and usually occur on the back of the hands. People may also experience scattered, waxy, hardened patches of skin, called pseudosclerosis.
The liver normally removes the toxic porphyrins from the blood and secretes them in bile. So, an increased number of porphyrins in the body can damage the liver.
People with PCT may develop problems such as hepatic siderosis, which is the accumulation of iron in the liver, and steatosis, the accumulation of fat in the liver.
Certain parts of the liver may become inflamed, or scarring may occur around the liver's portal vein. People with PCT may have a greater risk of developing cirrhosis (scarring of the liver) or liver cancer if the condition is left untreated.
Advanced liver disease is rare, although older people who have experienced multiple PCT attacks are at greater risk.
A blood test can help to diagnose PCT based on high levels of porphyrins in the clear blood plasma.
It can be difficult to diagnose PCT and to differentiate between the different kinds of porphyria. A doctor may recommend the following tests:
- A urine test to look for elevated levels of particular acids to rule out acute porphyria.
- A blood test to look for increased numbers of porphyrins in the clear, liquid part of the blood (plasma), which is a sign of PCT.
- A stool sample analysis to look for elevated levels of some porphyrins that may not be detected in urine samples. This can also help pinpoint the particular type of porphyria.
According to the American Porphyria Foundation, PCT is the most treatable of all the porphyrias.
The first step is to remove any aggravating factors, such as drugs containing estrogen.
Most people will then undergo a series of phlebotomies, procedures during which blood is removed from the body, with the aim of reducing the amount of iron in the body. Most people can expect to have around 5 or 6 pints of blood gradually removed, with 1 pint being removed every 1-2 weeks.
Doctors will measure the levels of ferritin (a protein that contains iron) and porphyrins in a person's blood to monitor improvement in the condition. Once ferritin levels fall to around 20 nanograms per milliliter (ng/ml), doctors can stop removing blood.
If taking blood is not an option, for example if the person has anemia, doctors can treat PCT with low doses of antimalarial medications, such as chloroquine or hydroxychloroquine.
After treatment, a doctor may want to continue to measure the levels of porphyrins in a person's blood, particularly if any estrogen therapy is resumed. This allows for any recurrent episodes to be treated quickly.
According to the American Porphyria Foundation, treatment of PCT is usually successful and the prognosis is excellent.
People with PCT should identify and avoid things that trigger the attacks, and follow recommendations made by their healthcare team.