Porphyria cutanea tarda

Porphyria cutanea tarda (PCT) is the most common form of porphyria. Patients with PCT have fragile skin and develop blisters on sun-exposed areas in response to minor trauma. Blisters are most common on the fingers, the face, and the back of the hands, and often cause scarring. Hair growth may increase, and the skin may gradually thicken and darken.

Porphyria cutanea tarda is caused by a defective enzyme (uroporphyrinogen decarboxylase), leading to a raised porphyrin concentration in the skin. It is diagnosed by measuring the plasma porphyrin concentration. About 75% of cases are sporadic (PCT-S), resulting from liver damage caused by iron overload, excessive alcohol consumption, hepatitis C infection, HIV infection, estrogen-containing preparations, and occupational or environmental hepatotoxins (eg dioxins). The remaining 25% of cases are familial (PCT-F); PCT-F has autosomal dominant inheritance and a younger age of onset.

Patients with PCT must avoid iron supplements, estrogen-containing preparations and alcohol. Strict sun protection is essential, with protective clothing, and broad-spectrum or reflective sunscreens (eg titanium dioxide). Sunscreens that do not block longer wavelength ultraviolet A and visible light are not effective. Phlebotomy is the standard treatment, sometimes in conjunction with low-dose hydroxychloroquine.