Porphyria cutanea tarda (PCT) is the most common of the hepatic porphyrias. It is due to reduced activity of the enzyme uroporphyrinogen decarboxylase (UROD), causing the subsequent build-up of uroporphyrinogen in the blood and urine (figure 1) . PCT has both sporadic and inherited (autosomal dominant) forms that are indistinguishable clinically. Hepatic UROD enzyme activity is diminished in both disorders. However, erythrocyte UROD activity levels are reduced only in the inherited form .
The clinical manifestations of PCT and the etiologic relation of the sporadic form to hepatitis C virus (HCV) infection will be reviewed here. General characteristics of PCT and the inherited porphyrias, including diagnosis and treatment, are discussed elsewhere. (See "Porphyrias: An overview" and "Porphyria cutanea tarda and hepatoerythropoietic porphyria".)
The skin and the liver are the two main sites affected in sporadic PCT as the classic presentation consists of photosensitivity and uroporphyrinuria in the setting of chronic liver disease. Several observations support the hypothesis that environmental triggers are necessary to provoke an attack of PCT. When families of patients with inherited PCT have been studied, for example, first-degree relatives often have decreased uroporphyrinogen decarboxylase (UROD) activity despite having no symptoms of PCT . Patients with sporadic PCT, on the other hand, may have normal UROD activity in between attacks . Possible triggers of PCT include polyhalogenated hydrocarbons (such as hexachlorobenzene), alcohol, estrogens, and iron overload [4-8]. (See "Porphyria cutanea tarda and hepatoerythropoietic porphyria", section on 'Etiology and pathogenesis'.)
Skin lesions — Skin lesions are frequently the reason that patients with either form of PCT first seek medical attention. Exposure to the sun and/or minor trauma can lead to skin erythema and the development of vesicles and bullae that may become hemorrhagic. Hyperpigmentation, hypopigmentation, hirsutism, and sclerodermatous changes may develop with the passage of time (picture 1) .
Liver disease — Chronic liver disease is common in sporadic PCT. Liver biopsy shows a wide range of changes, including steatosis, mild to severe inflammation, hepatic fibrosis, and cirrhosis . Hepatocellular carcinoma, usually in the presence of cirrhosis, also occurs with increased frequency . In contrast, liver involvement appears to be infrequent in inherited PCT . One small study, for example, found no liver disease in five such patients .