Understanding the Clinical Spectrum of the Cutaneous and Acute Hepatic Porphyrias.

Porphyrias are rare metabolic disorders caused by inherited or acquired enzymatic defects in the heme biosynthesis pathway, resulting in the accumulation of heme precursors or toxic porphyrin intermediates. The cutaneous porphyrias arise from enzymatic defects in later steps of the heme biosynthesis pathway, which lead to the build-up of photoactive porphyrins in the skin and liver, such as coproporphyrins, protoporphyrins, and uroporphyrins. These photoactive porphyrins generate reactive oxygen species that drive the characteristic cutaneous manifestations, including painful photosensitivity, skin fragility, and blistering. The cutaneous porphyrias encompass both blistering and non-blistering subtypes, which include erythropoietic protoporphyria, X-linked protoporphyria, congenital erythropoietic porphyria, porphyria cutanea tarda, and hepatoerythropoietic porphyria, each distinguished by specific biochemical patterns and clinical features. Acute hepatic porphyrias, which include acute intermittent porphyria, variegate porphyria, hereditary coproporphyria, and aminolevulinic acid dehydratase deficiency porphyria, result in the accumulation of neurotoxic precursors, such as δ-aminolevulinic acid and porphobilinogen. While acute neurovisceral attacks predominate in acute hepatic porphyrias, certain subtypes, such as variegate porphyria and hereditary coproporphyria, may present with blistering photosensitivity, creating a significant diagnostic overlap between cutaneous porphyrias and other photodermatoses. This overlap underscores the importance of awareness of acute hepatic porphyrias among dermatologists, who may be the first clinicians to encounter patients with these disorders. In addition, recent treatment breakthroughs will likely bring patients with porphyrias to pursue care, changing the likely underestimated disease prevalence rates. This narrative review provides a comprehensive overview of the pathobiology, clinical features, diagnostic strategies, and management approaches for the cutaneous and acute hepatic porphyrias.