Porphyria cutanea tarda
Porphyria cutanea tarda (PCT) is the most common form of porphyria that presents as painful blistering on sun-exposed areas of the skin, commonly the dorsum of hands, forearms, the back of the neck, and the face. Other clinical manifestations include hypertrichosis of the face, scarring, skin fragility, and photo-onycholysis (separation of nails from nailbed).
This disorder is caused by a deficiency in the enzyme uroporphyrinogen III decarboxylase (UROD). In most cases of PCT, liver toxicity (hepatitis C, alcohol abuse, exogenous estrogen exposure, hemochromatosis, other causes of iron overload, or hepatic tumors) causes or exacerbates the effects of the enzymatic deficiency. Uroporphyrins subsequently accumulate in the liver and the skin. At certain wavelengths of light (such as sunlight), the porphyrins in the skin release energy, and the reactive oxygen species cause tissue damage. Liver involvement includes focal steatosis, focal lobular necrosis, and portal inflammation and fibrosis.