Porphyria cutanea tarda (PCT) is the most common porphyria. It is inherited as an autosomal dominant disorder in 20% of cases and is acquired in association with other disorders in the remaining 80% of cases. PCT is related to a deficiency of the enzyme uroporphyrinogen decarboxylase.
- Stop exacerbating drugs (estrogens, OCPs, iron).
- Counsel the patient to stop all alcohol ingestion.
- Inform the patient that sunlight is a cofactor, and have the patient protect the skin from the sun until therapy has lowered porphyrin levels. Sunscreens are inadequate. Opaque physical blocks are required.
- Obtain a baseline 24-hour urine quantitative porphyrin level to guide therapy.
- Evaluate for hepatocellular disease with a physical examination and LFTs, a hepatitis C serology, and an assay for the hemochromatosis gene. Hepatitis C infection and hepatoma may precipitate porphyria cutanea tarda.
- In the nonanemic patient, repeated venesection of 400-500 ml of blood every 2-4 weeks may be performed. Hospitalized patients may have more frequent phlebotomies.
- Low-dose chlorquine 125 mg 2 times/week is quite effective. Check the LFTs, then give a test dose of chlorquine 125 mg, and recheck the LFTs before instituting therapy. Hydroxychlorquine 250 mg twice weekly may also be used.
- PCT patients on dialysis may be treated with erythropoietin.
- Phlebotomy is continued until clinical improvement occurs, keeping the hemoglobin in the 10- to 11-g range. Urine porphyrins fall with phlebotomy and may continue to fall for months after phlebotomy is discontinued.
- Antimalarial therapy is continued until urinary porphyrins are less than 300 mg/24 hours. Monitor LFTs monthly.
- Antimalarial therapy may be combined with repeated large or small phlebotomies in patients not responding to a single modality treatment alone.
- Do not give iron to correct the anemia induced by phlebotomy.
- Higher doses of antimalarials may induce a severe hepatotoxic crisis, with fever, chills, vomiting, and elevated LFTs.
- A clinically and histologically identical syndrome with normal porphyrins (pseudoporphyria) may be induced by certain phototoxic agents, notably tetracycline, NSAIDs, and estrogen. Urinary porphyrins are required to establish the correct diagnosis. Patients on dialysis may develop true porphyria or pseudoporphyria. Plasma and stool porphyrin levels are needed for diagnosis in this setting.
- Nonopaque sunscreens are not protective, as the active spectrum is at 400-410 nm, the borderline of long UV and visible violet radiation (Soret band).
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