Spectral Region of Photosensitivity in Hydroa Aestivale Seu Vacciniforme with Porphyrinuria

Abstract

Many attempts have been made to produce typical lesions in Hydroa patients by exposure to light, but few, if any, have succeeded in demonstrating a definitely increased sensitivity to light. Nevertheless, it has been very generally assumed that such patients are abnormally photosensitive and that porphyrins, which are found in the urine of many of these cases, are the photosensitizing substances. The present experiments would seem to demonstrate the truth of both these assumptions, and also to explain the discrepancies in the findings of others.

A boy of 7 years, suffering from Hydroa and displaying marked porphyrinuria, was subjected to exposure of small areas of the back to bright sunlight for 30 minutes, certain of the areas being covered with glass color filters to delimit various spectral regions. At the end of this time, a distinct erythema was observed on those areas which had received any considerable amount of radiation of wave lengths between approximately 3200 Å and 4500 Å, but not on the areas from which this portion of the sunlight had been excluded by the filters. The response occurred when the radiation shorter than 3200 Å, to which normal skin is sensitive, was excluded. Thus the skin of this patient is shown to be abnormally sensitive to light, responding to the spectral region between 3200 Å and 4500 Å, to which normal skin is not sensitive.

If we examine the absorption spectrum of porphyrins, we find a nice correspondence with the region of sensitivity of our patient, which may be taken as reasonable proof that porphyrins are the photosensitizing substance. Their most characteristic absorption lies between 3200Å and 4300 Å, 1 and this absorption is much greater than that which occurs in the visible spectrum. This accounts for the fact that longer wave lengths did not produce any response in the patient, although it is quite certain that prolonged exposure would have demonstrated some sensitivity in the visible portion of the spectrum.