Evaluation of the minimal erythema dose for UVB and UVA in context of skin phototype and nature of photodermatosis.

ABSTRACT

BACKGROUND: Phototesting is part of the standard procedure for the evaluation of patients with photosensitivity disorders. The response of patients to targeted UVB or UVA radiation helps to find out more about the nature of photodermatosis. Nevertheless, there are no default values of the minimal erythema dose (MED). METHODS: This study evaluated data of 203 patients (131 female, 72 male, mean age 52 years) who were referred for phototesting to the University Hospital Zurich between 2012 and 2017. We retrospectively analyzed the demographic data, medical history, skin phototype, reaction to UVB and UVA radiation, and, if present, the diagnosis of photodermatosis. In patients who did not develop erythema at the highest tested UV doses, the next logical increment was taken for analysis. In case of UVA, the two periphery doses could not be evaluated due to technical issues, so the closest reliable UVA doses were used. RESULTS: The MED-UVB correlated with the skin type and increased with a higher phototype. No such correlation could be seen for MED-UVA. However, the MED-UVA was significantly reduced in patients with photodermatosis without significant differences between the subgroups of photodermatosis. More than half of the patients did not show a reduced MED despite a diagnosed photodermatosis. CONCLUSION: We showed, how different skin types with and without photodermatosis react to UV radiation. Based on the results, we suggested threshold doses that can be chosen for phototesting, presented which doses can be considered pathologic and showed the probability of a pathologic MED in correlation with a diagnosed photodermatosis.