Definition of Porphyria Cutanea Tarda
Porphyria cutanea tarda: Literally, the late skin form of porphyria, a genetic photosensitive (light-sensitive) skin disease with onset in adult life with substances called uroporphyrins in the urine due to a deficiency of uroporphyrinogen decarboxylase (UROD), an enzyme required for the synthesis of heme (part of hemoglobin, the pigment in red blood cells that carries oxygen). The hallmarks of porphyria cutanea tarda (PCT) are blisters which become ulcerated in areas of the skin exposed to sunlight, especially on the face, ears and dorsum (back) of the hands. The affected areas of skin also tend to be fragile and show hyperpigmentation (excess pigment) and hypertrichosis (excess hair).
*Porphyria facts medically edited by William C. Shiel Jr., MD, FACP, FACR
- Porphyria is a group of diseases that are due to the deficiency of one of the enzymes needed to make an important substance in the body called heme.
- Porphyrias are often classified as acute or cutaneous. Acute types of porphyria affect the nervous system, whereas cutaneous types mainly affect the skin.
- Most porphyrias are inherited disorders.
- People with cutaneous forms of porphyria develop blisters, itching, and swelling of their skin when it is exposed to sunlight. Those with acute forms of porphyria develop numbness, tingling, paralysis, cramping, vomiting, constipation, personality changes or mental disorders, and/or pain in the abdomen, chest, limbs, or back.
- Doctors diagnose porphyria using blood, urine, and stool tests.
- Treatment may involve avoiding triggers, receiving heme through a vein, taking medicines to relieve symptoms, or having blood drawn to reduce iron in the body. People who have severe attacks may need to be hospitalized.
What is porphyria?
Porphyria is a term that refers to a group of disorders -- the porphyrias -- that affect the nervous system or skin, or both. Each type of porphyria is due to the deficiency of one of the enzymes needed to make a substance in the body called heme. Enzymes are proteins that help chemical reactions happen in the body. Making heme involves a series of eight different enzymes, each acting in turn.
Heme is a red pigment composed of iron linked to a chemical called protoporphyrin. Heme has important functions in the body. The largest amounts of heme are in the blood and bone marrow in the form of hemoglobin within red blood cells. Hemoglobin gives blood its red color and carries oxygen from the lungs to all parts of the body. In the liver, heme is a component of proteins that have many functions, including breaking down hormones, drugs, and other chemicals and generating high-energy compounds that keep liver cells alive and functioning normally.
The body makes heme mainly in the bone marrow and the liver. The process of making heme is called the heme biosynthetic pathway. Each step of the process is controlled by one of eight enzymes. If any one of the enzymes is deficient, the process is disrupted. As a result, porphyrin or its precursors - chemicals formed at earlier steps of the process -- may build up in body tissues and cause illness.