Porphyria cutanea tarda (PCT) is the most common of the cutaneous porphyrias. It is not associated with acute neurological attacks.
Deficient enzyme: uroporphyrinogen decarboxylase
Genetic locus: 1q34
(1) familial, with autosomal dominant inheritance
(2) sporadic, associated with some form of liver disease (more common type)
Cutaneous manifestations - primarily affect sun-exposed skin:
(1) photosensitivity with fragility and subepidermal blistering
(2) skin lesions may scar or become infected
(3) violaceous or melasma-like pigmentary changes, especially on the face
(4) hypertrichosis, especially over the forehead and upper cheeks
(5) presence of milia, especially over the face
(6) sclerodermoid plaques
(7) dystrophic calcification
(8) scarring alopecia
(10) poor wound healing
Urinary color changes (may require acidification or solvent extraction):
(1) reddish brown color
(2) pink fluorescence under ultraviolet light (with a Woods lamp)
A liver biopsy may fluoresce under ultraviolet light.
(1) The urine shows increased uroporphyrins and coproporphyrins with uroporphyrins levels much greater than the coproporphyrins
(2) The feces show increased uroporphyrins and isocoproporphyrins
(3) Erythrocytes do not show elevated protoporphyrins.
(4) Porphobilinogen and aminolevulinic acid are not increased in the urine.
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Specialty: Endocrinology, Clinical Laboratory, Gastroenterology