Porphyria Cutanea Tarda (PCT) is the most common form of porphyria. The disease develops in midlife with a mean age of 45 years at onset. It is characterized by photosensitivity (sensitivity to sun exposure) resulting in bullae (blisters), milia, and scarring. The dorsal hands and forearms, ears and face are primarily affected.
The bullae are noninflammatory and rupture easily to form erosions and shallow ulcerations. These often heal with scarring, milia, and dyspigmentation. Patients experience skin fragility. Hyperpigmentation often follows especially on the face, neck and hands. Hypertichosis (excessive hair growth) of the face is seen particularly over the cheeks and temple regions. Liver disease is frequently found and the patient in the first image above had hemochromatosis and PCT.
CAUSE: PCT is caused by a deficiency in the enzyme uroporphyrinogen decarboxylaase (UROD) and enzyme utilized in synthesizing the red pigment in red blood cells. PCT has frequently been associated with other diseases such as type 2 diabetes, alcoholism, systemic lupus, HIV disease and estrogen therapy. Several other types have been described, the most common of these is the sporadic, nonfamilial form, which represents about 75-80% of cases. UROD activity is abnormal in the liver but normal in other tissues. UROD function is inhibited by iron so any condition that promotes iron overload in the liver (cirrhosis, alcoholism, HCV infection, type 2 diabetes and hemochromatosis) are associated with PCT. Iron overload is frequently an issue and improvement occurs upon removal. The second most common form is inherited in an autosomal dominant fashion resulting in about a 50% reduction in concentration and activity of UROD. In inherited forms the disease manifests at an earlier age and onset before the age of 20 strongly suggests an inherited form.
Why does the sun cause blistering and skin damage? The buildup of porphyrins in tissue is the problem. Porphyrins exposed to the “Soret band” which is 400 nm, within the UVA wavelengths of light, damages skin cells resulting in blistering and skin fragility.
DIAGNOSIS: The diagnosis is based on clinical impression, skin biopsy and 24 hour urine collection for detection of porphyrins.
TREATMENT: A number of interventions need to be applied first, such as removal of all precipitating environmental agents such as alcohol and medications that may be involved. Sun protection protocols should be followed–avoid sun exposure, use of physical barriers such as hats and gloves and use of UVA protection sunscreens, such as titanium or zinc oxide based products. Phlebotomy (blood draws) is highly effective treatment–500 ml at 2-week intervals performed until hemoglobin values reach 10 g/dL or the serum iron values reach 50-60 micro-grams/dL. This process takes several months to control the cutaneous features of PCT. Oral iron replacement therapy should not be administered to these patients once target values have been obtained, a frequent provider error.