[Porphyria cutanea tarda (PCT)].

Porphyria cutanea tarda (PCT) can be divided into two genetically determined (hereditary) forms and one acquired type. Hereditary PCT is due to an inborn deficiency of the uroporphyrinogen decarboxylase activity in all tissues. The homozygote defect (porphyria hepatoerythropoetica) involves reduced enzyme activity down to nearly 5%, whereas the hemizygote form causes reduction of the porphyrinogen decarboxylase activity of about 50%, which means that the remaining enzyme activity is still sufficient for normal heme or porphyrin biosynthesis. Only an overload of heme or porphyrin biosynthesis leads to decompensation of the uroporphyrinogen decarboxylase. Substances able to act in this way are: ethanol, lipophilic drugs, xenobiotics, steroid hormones, and iron. Sporadic (acquired) PCT is associated with reduction of the uroporphyrinogen decarboxylase activity in the liver exclusively induced by the above cited chemicals. From these types of PCT, pseudo-PCT (or PCT-like syndrome) must be differentiated. Pseudo-PCT is observed in patients with terminal renal insufficiency under hemodialysis therapy as well as after application of certain drugs. Pseudo-PCT can be separated from PCT by means of porphyrin analysis and histopathological findings.