Porphyria Types
Porphyria Cutanea Tarda (PCT)
This disease is the most common of the porphyrias and results
from a deficiency of the enzyme, uroporphyrinogen decarboxylase
(UROD). PCT is essentially an acquired disease, but some individuals
have a genetic (autosomal dominant) deficiency of UROD that contributes
to its development. These individuals are referred to as having "familial
PCT". Most individuals with the inherited enzyme deficiency
remain latent and never have symptoms.
PCT is one of the hepatic porphyrias. Large amounts of porphyrins
build up in the liver when the disease is becoming active. The
disease becomes active when acquired factors, such as iron, alcohol,
hepatitis C virus (HCV), HIV,estrogens (used, for example, in oral
contraceptives and prostate cancer treatment) and possibly smoking,
combine to cause a deficiency of UROD in the liver. Hemochromatosis,
an iron overload disorder, also can predispose individuals to PCT.
Symptoms
The symptoms in PCT are confined mostly to the skin. Blisters
develop on sun-exposed areas of the skin, such as the hands and
face. The skin in these areas may blister or peel after minor trauma.
Increased hair growth, as well as darkening and thickening of the
skin may also occur. Neurological and abdominal symptoms are not
characteristic of PCT.
Liver function abnormalities are common but are usually mild.
These sometimes progress to cirrhosis and even liver cancer. PCT
is often associated with hepatitis C infection, which also can
cause these liver complications. However, liver tests are generally
abnormal even in PCT patients without hepatitis C infection.
Diagnosis
The preferred screening test for PCT is a measurement of porphyrins in plasma.
This can differentiate PCT from variegate porphyria. The patterns of porphyrins
in urine (predominately uroporphyrin and 7-carboxylate porphyrin) and feces
(predominately isocoproporphyrin) help to confirm the diagnosis. The presence
of an inherited deficiency of UROD can be demonstrated by measuring the enzyme
in red blood cells and is present in about 20% of patients with PCT
Treatment and Prognosis
PCT is the most treatable of the porphyrias. Treatment seems to be equally
effective in familial and non-familial PCT. Factors that tend to activate
the disease should be removed. The most widely recommended treatment is a
schedule of repeated phlebotomies (removal of blood), with the aim of reducing
iron in the liver. This actually reduces iron stores throughout the body.
Usually, removal of only 5 to 6 pints of blood (one pint every one to two
weeks) is sufficient, which indicates that iron stores are not excessively
increased in most PCT patients. The best guides to response are measurements
of serum ferritin and plasma porphyrins. Phlebotomies are stopped when the
ferritin falls to -~20ng/ml. Another treatment approach is a regimen of low
doses of either chloroquine (125mg twice weekly) or hydroxychloroquine (100mg
twice weekly). Usual dosages of these drugs should not be used because they
can cause transient but sometimes severe liver damage and worsening of photosensitivity
in PCT patients. Recurrences can be treated in the same manner. But PCT usually
does not recur after treatment. It is not necessary to continue phlebotomies
after a remission has been achieved.
For more information please see PCT.
|
