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| Fig. 37.8 Vesicles and blisters, some hemorrhagic, on the digits of a patient with porphyria cutanea tarda. |
Porphyria cutanea tarda (PCT) is a metabolic disease characterized by skin fragility, chronic blistering, and scarring of the dorsal hands, forearms, ears, and face associated with photosensitivity to sunlight (Fig. 37-8). In addition to the blistering and scarring, skin findings include thickened, coarse hairs (hypertrichosis) over the temples, forehead, and cheeks; occasional shiny, thickened, scleroderma-like changes of the face, scalp, posterior neck, and torso; and hyperpigmentation or hypopigmentation.
PCT is either of autosomal dominant inheritance with incomplete penetrance or is acquired. There is a high incidence of liver disease and iron overload in patients with PCT. Factors that may trigger attacks of PCT include alcohol abuse, hepatitis C infection, estrogens (especially oral contraceptives), and HIV infection. The biochemical defect in chromosome 3q12 (
UROD gene) leads to a deficiency of the hepatic and red blood cell enzyme uroporphyrinogen decarboxylase. This is the fifth enzyme in the metabolic pathway of the synthesis of hemoglobin.
The liver’s resultant overproduction of porphyrin precursors (photosensitizing compounds) causes a thickening of the dermal vascular architecture following exposure to sunlight.
A useful laboratory test that can be performed in the office is the demonstration of pink-red fluorescence of the patient’s urine when exposed to ultraviolet light. A Wood’s light emitting ultraviolet A (UVA) can be used for this test. Patients also have increased total body iron stores reflected in increased serum iron and ferritin levels. Quantitative measurement of the urine porphyrins in a 24-hour urine specimen will confirm the diagnosis. Treatment of PCT includes elimination of alcohol and other predisposing medications, photoprotection, phlebotomy, and low-dose antimalarial therapy (chloroquine).
Kauppinene R: Porphyrias, Lancet 365 (9455):241–252, 2005.
