PATTERN-ANALYSIS OF PHOTOPATCH TEST REACTIONS

In a multicenter study, photopatch test results from more than 1500 pa tients were evaluated between 1985 and 1990 and from 614 patients betw een 1990 and 1992. Photopatch testing was conducted according to a sta ndardized procedure. Nearly half of the photoreactions were unclassifi able according to the classic definitions of photoallergic or phototox ic reactions. To facilitate the interpretation of these remaining phot opatch test reactions, we developed a computerized substance specific reaction pattern analysis. By sequential readings from immediately aft er irradiation up to 72 h later and by morphological qualification of the reactions, the time course and morphological changes of each indiv idual reaction were monitored. The summation of each individual photor eaction resulted in an overall reaction pattern of a specific substanc e. Four main categories could be distinguished. The first category was characterized by a peak immediately after irradiation followed by a d ecrescendo reaction. The second category comprized reactions combining an immediate with a delayed reaction. The third category exhibited a plateau-like delayed reaction. The fourth category showed delayed reac tions in a crescendo pattern. Whereas category 1 represents classic ph ototoxic and category 4 classic photoallergic reaction patterns, the u nderlying mechanisms of categories 2 and 3 remain to be investigated. Typical substances of category 1 were many of the tested systemic drug s, such as furosemide, most of which are well-known phototoxic agents. Disinfectants, nonsteroidal anti-inflammatory agents and phenothiazin es showed the reaction patterns of categories 2 and 3, A delayed-type reaction (category 4) could be demonstrated for well-known photoallerg ens such as fenticlor, musk ambrette, and ultraviolet adsorbents in su nscreens. To prove the specifity of the cumulative reaction patterns, a second test series was analyzed, including 614 patients. Comparison of the reaction patterns from 1985-1990 with the reaction patterns fro m 1990-1992 showed in most cases a virtual indentity. Therefore, it is concluded that pattern analysis reveals a characteristic feature of a given substance, opening new aspects for evaluation of photosensitizi ng substances.