The porphyrias represent a group of metabolic disorders in which there is dysfunction of the enzymes involved in heme synthesis (Fig. 41.1). With the exception of acquired porphyria cutanea tarda (PCT), the underlying etiology is monogenetic mutations. Porphyrins absorb light energy (400–410 nm) and their accumulation within the skin can lead to photosensitization, with water-soluble porphyrins producing blisters and lipophilic porphyrins leading to acute burning and erythema. This chapter focuses on those porphyrias with cutaneous manifestations.

Porphyria Cutanea Tarda (PCT)

• The most common form of cutaneous porphyria; clinical findings typically appear during the 3rd to 4th decade of life.

• Dysfunction of uroporphyrinogen decarboxylase (UD) is usually acquired (type I) but can be inherited in an autosomal dominant manner (type II); the ratio of type I : type II is ~3 : 1.

• In type I PCT, the enzyme is only dysfunctional in the liver, rather than in all tissues; hepatotoxins (e.g. alcohol, iron overload), hepatitis C virus, HIV infection, or estrogens can precipitate or exacerbate PCT.

• In addition to photosensitivity, characteristic skin findings include fragility, erosions, vesicobullae, milia, and scars in sun-exposed areas, especially on the dorsal aspects of the hand (Fig. 41.2); hypertrichosis (malar region) and hyperpigmentation can develop on the face (Fig. 41.3); morpheaform plaques are seen less often (Fig. 41.4).

Fig. 41.2 Porphyria cutanea tarda. A Marked fragility with multiple hemorrhagic crusts, erosions, and milia as well as scars. B Flaccid bulla and tense vesicle with clear fluid on the forefinger, accompanied by crusts and scars. B, Courtesy, Jorge Frank, MD, and Pamela Poblete-Gutiérrez, MD.

Fig. 41.3 Porphyria cutanea tarda. Hypertrichosis of the malar region of the cheek. Courtesy, Judit Stenn, MD.

Fig. 41.4 Porphyria cutanea tarda presenting as yellow-brown morpheaform plaques. The plaques were in sun-exposed areas in this patient with a history of alcohol abuse.

• Histologically, if a bulla is biopsied, there is a subepidermal split with minimal inflammation; thickened basement membranes around capillaries in the dermis with festooning of the dermal papillae are also seen.

• Diagnosis is based on the detection of elevated levels of urinary uro- and coproporphyrins (water-soluble) or elevated plasma uroporphyrins or fecal isocoproporphyrins; genetic analysis can be performed for type II PCT.

• Additional evaluation includes serum ferritin and if elevated, analysis of the hemochromatosis gene, screening for hepatitis B or C viral infection, and if risk factors, HIV infection.

• DDx: pseudoporphyria due to medications (Table 41.1

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