Protoporphyrin IX in the skin measured noninvasively predicts photosensitivity in patients with erythropoietic protoporphyria.

Abstract

Erythropoietic protoporphyria (EPP) is a rare genetic disease that causes severe sensitivity to visible light as a result of protoporphyrin IX (PpIX) accumulation in the skin. To establish a noninvasive method to measure PpIX in the skin of patients with EPP and to investigate how skin PpIX relates to erythrocyte PpIX and photosensitivity. Skin PpIX was measured in 25 patients with EPP by calculating the difference in PpIX fluorescence before and after complete photobleaching of PpIX using controlled illumination. The patients reported symptoms during the illumination and skin erythema was measured before and after illumination. Confirmation of the presence of PpIX was obtained in seven patients by measuring the in vivo fluorescence emission spectrum. This method was used to examine skin PpIX during the hours after an illumination in seven patients. We established a noninvasive method to measure skin PpIX based on measurements of PpIX fluorescence before and after complete PpIX photobleaching. The patients had an average skin PpIX of 2·0 units and skin emission spectra confirmed the presence of skin PpIX (peak emission 632 nm). Skin PpIX was associated with erythrocyte PpIX (P = 0·002, R2 = 0·34), skin erythema (P = 0·001, R2 = 0·47) and symptoms during illumination. Furthermore, skin PpIX increased during the hours after illumination. We have developed a noninvasive method to measure skin PpIX in patients with EPP. Skin PpIX is dependent on erythrocyte PpIX and exposure of the skin to light. This method can be used for objective monitoring of treatment effect.