To the Editor.—
A letter by Mathews-Roth et al, published in the Archives (1979;115:1391-1392), describes a phototesting procedure that is presented as an objective, reproducible means of testing therapeutic efficacy of oral beta carotene in patients with erythropoietic protoporphyria (EPP). We maintain that the authors have not verified that their technique is reproducible or that it measures therapeutic efficacy, as we understand the terms. Apparently, the authors based their claims on two facts: that patients with EPP who obtained increased sunlight tolerance during beta carotene treatment also had increased tolerance to a modified solar simulator and that patients without clinical improvement did not have increased tolerance to the artificial light source. The reader should recognize that this type of distinction is qualitative rather than quantitative. To clarify this point, a positive qualitative result simply indicates the patient has increased sunlight tolerance; it does not disclose the magnitude of the increase.
Fusaro RM, Johnson JA. Phototesting of Patients With Erythropoietic Protoporphyria. Arch Dermatol. 1981;117(4):190–191. doi:10.1001/archderm.1981.01650040004006