By Afsaneh Khetrapal, BSc (Hons)
Porphyria cutanea tarda (PCT) belongs to group of disorders named the porphyrias. A porphyria is characterized by the abnormal metabolism of the blood pigment hemoglobin.
In porphyria, cells fail tconvert porphyrins and porphyrin precursors intheme. This biosynthetic pathway for this relies on the functioning of eight enzymes for the appropriate synthesizing of heme. Thus, a deficiency in even one of these enzymes could result in the accumulation of porphyrins and porphyrin precursors that then cause illness.
PCT is the most common form of porphyria and results from a dysfunctional enzyme within the liver named uroporphyrinogen decarboxylase (UROD). PCT is subdivided intType 1 (sporadic PCT) and Type 2 (familial PCT).
Approximately 75-80% of PCT cases are classified as Type 1. These generally begin midway in adulthood following exposure tparticular chemicals now known televate the synthesis of heme precursors (porphyrins) in the liver. The factors which trigger the acquired disorder include:
- Moderately heavy alcohol consumption
- Artificial estrogens - often in the form of oral contraception (e.g. birth control), hormone replacement therapy, liver disease, and prostate cancer treatment
- Iron overload which can possibly result from;
- High intake - often via oral supplementation or blood transfusion
- Viral infections - HIV or hepatitis (especially chronic hepatitis C)
- Hereditary hemochromatosis - thus gene abnormalities associated with this are trigger factors. This chronic blood disorder is alsthe most common disease resulting in over absorption of iron
Type 2 PCT shows association with mutation in the gene encoding UROD and significantly less with trigger factors. Interestingly, some people whhave the causal gene mutations for Type 2 PCT are affected by a latent form of this porphyria. i.e. they exhibit none of the symptoms of PCT. Unfortunately, those whdsuffer from the symptoms experience the onset of this at a younger age than in type 1 PCT. The general symptoms of porphyrias are as follows:
- Hypersensitivity tsunlight exposure - this leads titching and swelling of sun-exposed areas. Thus, it is recommended in some necessary cases tavoid direct sunlight as much as possible. Protect skin from sunlight by wearing light cotton gloves, long sleeves, and a hat.
- Sores (erosions) following relatively minor injuries
- Fluid filled blisters (vesicles and bullae) eventually healing tform small cysts (milia)
PCT is the most treatable form of the porphyrias. Furthermore, the treatment of PCT is almost always successful, and the prognosis is usually excellent. Treatment involves the removal of the aforementioned factors responsible for activating the disease in the first place. Fortunately, such action appears tbe effective in both familial and sporadic PCT equally.
The main treatment involves a schedule of blood removal via repeated phlebotomy sessions which aim treduce the hepatic iron level. An alternative treatment may be a low dose regimen of anti-malaria drugs - twice weekly doses of chloroquine or hydroxychloroquine. It is important that these drugs are taken at a carefully selected dosage because otherwise they have the potential tinflict temporary but potentially serious liver damage.
Following appropriate treatment for PCT, the regular monitoring of plasma porphyrins levels may be recommended. It is of particular importance should a patient require a known trigger factor as part of their lifestyle or health choices, e.g. artificial estrogen present in birth control.
Reviewed by Susha Cheriyedath, MSc
Last Updated: Jun 24, 2016