ABSTRACT
Fluorescence emission maximum of diluted plasma at neutral pH, which differentiates variegate porphyria and erythropoietic protoporphyria from other cutaneous porphyrias. Measurement of plasma porphyrins or spectrofluorimetric scanning of diluted plasma at neutral pH will detect active cutaneous porphyrias and are useful for screening. Porphyria cutanea tarda (PCT) may occur with other conditions predisposing to iron overload, and with diabetes mellitus. PCT occurs more commonly than expected in patients with cutaneous and systemic lupus erythematosus, precipitated by antimalarial therapy such as chloroquine which is porphyrogenic. Patterns of individual porphyrins in plasma, erythrocytes, urine and stool and porphyrin precursors in urine help explain the clinical features of the porphyrias and allow the diagnosis of each to be made by biochemical methods. PCT is due to an acquired deficiency of Uroporphyrinogen decarboxylase in the liver, although an inherited deficiency of the enzyme and other genetic factors sometimes contribute.
