Protoporphyrin IX in the skin measured non-invasively predicts photosensitivity in patients with erythropoietic protoporphyria

Summary

Background

Erythropoietic protoporphyria (EPP) is a rare genetic disease that causes severe sensitivity to visible light due to protoporphyrin IX (PpIX) accumulation in the skin.

Objectives

To establish a non-invasive method to measure PpIX in the skin of EPP patients and to investigate how skin PpIX relates to erythrocyte PpIX and photosensitivity.

Methods

Skin PpIX was measured in 25 EPP patients as the difference in PpIX fluorescence before and after complete photobleaching of PpIX by controlled illumination. Patients reported symptoms during the illumination and skin erythema was measured before and after. Confirmation of the presence of PpIX was obtained in 7 patients by measuring the in vivo fluorescence emission spectrum. The method was used to examine skin PpIX in the hours after an illumination in 7 patients.

Results

We established a non-invasive method to measure skin PpIX based on measurements of PpIX fluorescence before and after complete PpIX photobleaching. 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 = 0.0001; R² = 0.47) and symptoms during illumination. Furthermore, skin PpIX increased in the hours after illumination.

Conclusions

We have developed a non-invasive method to measure skin PpIX in EPP patients. Skin PpIX is dependent on erythrocyte PpIX and light exposure of the skin. This method can be used for objective monitoring of treatment effect.

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