Cutaneous porphyrias result from deficiency (and in one case, excess) of certain enzymes in the heme biosynthetic pathway (see table ), resulting in a relatively steady production of phototoxic porphyrins in the liver or bone marrow. These porphyrins accumulate in the skin and, on sunlight exposure (visible light, including near-ultraviolet [UV]), generate cytotoxic radicals that cause recurrent or unremitting cutaneous manifestations.
(See also Overview of Porphyrias.)
Cutaneous porphyrias include
Porphyria cutanea tarda (PCT)
Congenital erythropoietic porphyria (CEP—see table Some Less Common Porphyrias)
X-linked protoporphyria (XLPP), sometimes regarded as a clinical variant of EPP
Hepatoerythropoietic porphyria (HEP—see table Some Less Common Porphyrias), sometimes regarded as a type of PCT (extremely rare)
The acute porphyrias variegate porphyria (VP) and hereditary coproporphyria (HCP) may also have cutaneous manifestations.
In all cutaneous porphyrias except erythropoietic protoporphyria and X-linked protoporphyria, cutaneous photosensitivity manifests as fragile skin and bullous eruptions. Skin changes generally occur on sun-exposed areas (eg, face, neck, dorsal aspects of hands and forearms) or traumatized skin. The cutaneous reaction is insidious, and often patients are unaware of the connection to sun exposure. In contrast, the photosensitivity in erythropoietic protoporphyria and X-linked protoporphyria occurs within minutes or hours after sun exposure, manifesting as a burning pain that persists for hours, without any blistering and often without any objective signs on the skin. However, swelling and erythema may occur.
Chronic liver disorders are common in cutaneous porphyrias.
The cutaneous porphyrias are all accompanied by elevated total plasma porphyrins, and are specifically diagnosed by measurements of porphyrins in red blood cells, plasma, urine, and stool, as well as by genetic or enzyme analysis. Treatment involves avoidance of sunlight, measures to protect the skin, and sometimes other treatments directed according to the specific diagnosis.
