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Porphyria Cutanea Tarda
Porphyria cutanea tarda is the most common porphyria and causes blistering and fragility of skin exposed to sunlight.
Porphyria cutanea tarda occurs throughout the world. As far as is known, one form of this porphyria is the only one 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 excess iron in the liver, moderate or heavy alcohol use, smoking, taking estrogens , and infection with hepatitis C virus. 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.
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.
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 a week or two 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. 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.
Combining phlebotomy and chloroquine treatments accelerates improvement.
For women 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.
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