Diagnostic phototesting in the United Kingdom

Pbototesting is an essential part of tbe investigation of tbe pbotodermatoses. adding an objective basis for diagnosis to bistory and examination. A worksbop organized by tbe Britisb Pbotodermatology Group was beld recently to discuss current uses, methodology and problems of pbototesting, Tbe worksbop was designed to produce clarification of tbese points for tbe general dermatologist, as well as providing a forum for tbe critical examination of specific areas, including tbe possibilities for standardizing U.K. pbototest procedures. Techniques and uses of photopatch testing were not discussed. Pbototesting aids diagnosis through demonstration of abnormal responses in terms of wavelength dependence, exposure dose, morphology and time-course of the reactions produced. Repeat phototesting allows the natural progression of a disease to be monitored, or its response to treatment. Tbe phototesting techniques developed for diagnosis are also used for research and it is clear that interest in and developments of phototesting have resulted in advances in the understanding of the photodermatoses. Routine diagnostic phototesting is a procedure which remains restricted to a few centres in the U.K. Unlike patch testing, which is largely qualitative, phototesting must be quantitative if clinically useful results are to be obtained. This requires appropriate knowledge of light sources and their measurement, and for this reason collaboration with a medical physicist experienced in photophysics is desirable. The simplest and cheapest sources of ultraviolet and visible radiation are fluorescent lamps. The spectral emission from a fluorescent lamp is normally broad and as a consequence only crude information regarding wavelength sensitivity can be obtained. Fluorescent lamps with a significant UVB emission (e.g. Philips TL12) can be used to provide information on erythemal sensitivity^ with irradiation times of a few minutes. Unfortunately the exposure times using UVA fiuorescent