Porphyria Cutanea Tarda
Porphyria cutanea tarda is the most common porphyria and causes blistering and fragility of skin exposed to sunlight.
People have chronically recurring blisters on the sun-exposed areas of their bodies.
Excess iron can build up in the liver, causing liver damage.
Doctors test urine and stool samples for high levels of porphyrins.
Removing blood (phlebotomy), giving chloroquine (or hydroxychloroquine), or doing both is helpful.
Porphyria cutanea tarda occurs throughout the world.
In about 75 to 80% of people with porphyria cutanea tarda, the disorder does not appear to be hereditary and is called sporadic. In the remaining 20 to 25%, the disorder is hereditary and is called familial.
As far as is known, the sporadic form of this porphyria is the only porphyria that can occur in people who do not have an inherited deficiency of an enzyme involved in heme production.
Porphyria cutanea tarda results from underactivity of the enzyme uroporphyrinogen decarboxylase, which leads to accumulation of porphyrins in the liver. Liver disease is common. About 35% of people develop cirrhosis and 7 to 24% develop liver cancer. Skin damage occurs because excess porphyrins produced in the liver are transported by the blood to the skin.
Porphyria cutanea tarda has several common precipitating factors. These factors include
Infection with the human immunodeficiency virus (HIV) is a less common precipitating factor. These factors are thought to interact with iron and oxygen in the liver and thereby inhibit or damage the enzyme uroporphyrinogen decarboxylase.
Symptoms may not begin immediately after exposure to sunlight, so people may not realize that sun exposure is causing the symptoms.
People with porphyria cutanea tarda experience chronic, recurring blisters of various sizes on sun-exposed areas such as the arms, face, and especially the backs of the hands. Crusting and scarring follow the blisters and take a long time to heal. The skin, especially on the hands, is fragile and sensitive to minor injury.
Sometimes sun exposure causes swelling, itching, or redness. Hair growth on the face and other sun-exposed areas may increase.
To diagnose porphyria cutanea tarda, doctors test blood, urine, and stool for unusually high levels of porphyrins. The specific porphyrins that are increased provide a pattern that allows doctors to distinguish porphyria cutanea tarda from other porphyrias.
Doctors usually do tests to determine the factor that precipitated the development of porphyria cutanea tarda and to see whether there is too much iron in the liver. If people are not already known to have hepatitis C or HIV infection, doctors do tests for those disorders.
Porphyria cutanea tarda is the most readily treated porphyria. Avoiding alcohol and other precipitating factors is beneficial. People should avoid sun exposure as much as possible.
A procedure called phlebotomy, in which a pint (almost half a liter) of blood is removed, is the most widely recommended treatment. Doctors typically do 6 to 10 sessions of phlebotomy, with sessions two to four weeks apart. With phlebotomy, the excess iron is gradually removed, the activity of uroporphyrinogen decarboxylase in the liver returns toward normal, and porphyrin levels in the liver and blood fall gradually. The skin symptoms resolve.
Phlebotomy sessions are stopped when people become slightly iron deficient (or almost so). Anemia may develop if too many phlebotomy sessions are done or if sessions are done too frequently.
Very low doses of chloroquine or hydroxychloroquine are also effective in treating porphyria cutanea tarda. These drugs remove excess porphyrins from the liver by increasing their excretion in the urine. However, doses that are too high cause porphyrins to be removed too rapidly, resulting in a temporary worsening of the disorder and damage to the liver.
For people taking estrogen, doctors stop the estrogen therapy (because it is a precipitating factor of the porphyria) until phlebotomy has been completed and porphyrin levels are normal.