Section 12. Disorders of Nutrition and Metabolism

Chapter 160. Porphyrias

Topics: Introduction | Porphyria Cutanea Tarda | Acute Intermittent Porphyria | Erythropoietic Protoporphyria

Porphyria Cutanea Tarda

Porphyria cutanea tarda is the most common porphyria and causes blistering of skin exposed to sunlight.

Porphyria cutanea tarda occurs throughout the world. As far as is known, this porphyria is the only one that can occur in someone without 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. Skin damage occurs because porphyrins produced in the liver are transported by the blood plasma to the skin.

Several common factors (precipitating factors) are associated with porphyria cutanea tarda; these include excess iron in body tissues, moderate or heavy alcohol use, taking estrogens, infection with hepatitis C virus, and possibly smoking. 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 80% of people with porphyria cutanea tarda, the disorder does not appear to be hereditary and is called sporadic. In the remaining 20%, the disorder is hereditary and is called familial.

Symptoms and Diagnosis

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 also sensitive to minor injury. Hair growth on the face and other sun-exposed area may increase. Liver damage usually occurs; cirrhosis and even liver cancer may eventually develop.

To diagnose porphyria cutanea tarda, a doctor tests the blood plasma, urine, and stool for increased levels of porphyrins. The specific porphyrins that are increased provide a pattern that distinguishes porphyria cutanea tarda from other porphyrias.

Treatment

Porphyria cutanea tarda is the most readily treated porphyria. Avoiding alcohol and other precipitating factors is beneficial.

A procedure called phlebotomy, in which a pint of blood is removed, is the most widely recommended treatment. 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 plasma fall gradually. The skin symptoms improve, and the skin eventually returns to normal. Phlebotomy is discontinued when the person becomes slightly iron deficient. Anemia develops if too many phlebotomy sessions are performed.

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.

For women taking estrogen, doctors discontinue the estrogen therapy (because it is a precipitating factor of the porphyria) until phlebotomy has been completed and porphyrin levels are normal. The estrogen is then restarted and seldom causes a recurrence of the porphyria.