Light-Sensing Device May Help in Predicting EPP Symptoms

Study of wearable dosimeter for ultraviolet light, measuring patients' exposure

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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A wearable device capable of measuring light exposure could help to predict symptoms of erythropoietic protoporphyria (EPP), and may be useful as a measure to include in clinical trials, according to a recent study.

The study, “Prospective observational pilot study of quantitative light dosimetry in erythropoietic protoporphyria,” was published in the Journal of the American Academy of Dermatology.

EPP, caused by mutations in the FECH gene, is one of the most common types of porphyria. Like many other forms, EPP is commonly characterized by increased light sensitivity, and patients generally have to take steps to minimize sunlight exposure in order to reduce the risk of skin reactions.

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Dosimetry doses, on average, related well to patients’ reported light sensitivity

Clinical trials in EPP have often assessed light exposure by relying on participants reporting how much time they spent outdoors, but this can be imprecise and time-consuming.

“Self-reported light tolerance … is an imprecise and subjective measure although the best measure currently available,” the researchers wrote. “The current study seeks to move away from such subjective measures.”

A team led by researchers in the U.S. conducted a pilot trial where they used a technique called UV light dosimetry to assess light exposure in EPP patients. This was achieved with the help of a dosimeter, a device that detects ultraviolet light and can be worn by patients.

The study included 24 people with EPP. Participants wore the dosimetry device for one month, then for another month self-reported their outdoor exposure time via text messages. Throughout, patients provided detailed updates regarding their EPP symptoms.

The vast majority of participants completed all parts of the study according to protocol, suggesting that this method is feasible for patients. Due to technical errors, however, only about half of the planned dosimetry data was available for analyses.

Scientists conducted statistical tests to see how light exposure, as measured by dosimetry, was connected to patient-reported symptoms. Results showed there was a statistically significant relationship, with the connection to symptom severity being stronger for dosimetry than for patient-reported outdoor time. In these models, a one standard deviation increase in light dose measured by dosimetry increased the odds of having symptoms by 70%.

Mean dosimetry dose for each patient showed statistically significant relationships with their self-reported light sensitivity. However, patient-reported outdoor time did not significantly associate with self-reported light sensitivity.

“This study demonstrates that device dosimetry provides a superior measure of EPP patients’ light tolerance and better estimate of symptom risk as compared to self-reported outdoor time,” the scientists wrote, adding that this study, “lays important groundwork for future studies of light dosimetry in EPP, which will be critical both for clinical trial endpoints and for predicting and preventing symptoms.”