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Knowledge of Body Site Variability in Ultraviolet-Induced Erythemal Responses Guides Choice of Site for Pre-Therapy Minimal Erythema Dose Testing

2005; Elsevier BV; Volume: 124; Issue: 3 Linguagem: Inglês

10.1111/j.0022-202x.2005.23619.x

1523-1747

Robert Dawe,

melanin and skin pigmentation

minimal erythemal dose To the Editor: Waterston et al., 2004Waterston K. Naysmith L. Rees J.L. Physiological variation in the erythemal response to ultraviolet radiation and photoadaptation.J Invest Dermatol. 2004; 123: 958-964Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar have confirmed that there is marked variability between body sites in ultraviolet-induced erythemal responses. Although there are differences in erythemal responses to different ultraviolet wavebands (Olson et al., 1966Olson R.L. Sayre R.M. Everett M.A. Effect of anatomic location and time on ultraviolet erythema.Arch Dermatol. 1966; 93: 211-215Crossref PubMed Scopus (57) Google Scholar), their findings are in line with those of the earlier studies in which unfiltered mercury arc lamps (Schall and Alius, 1926Schall L. Alius H.-J. Zur Biologie des Ultraviolettlichts. Die Reaktion der menslichen Haut auf die Ultraviolettlichtbestrahlung (Erythemablauf).Strahlentherapie. 1926; 23: 161-180Google Scholar; Wucherpfennig, 1931Wucherpfennig V. Biologie und praktische Verwendbarkeit der Erythemschwelle des UV.Strahlentherapie. 1931; 40: 201-244Google Scholar) and a xenon arc monochromator delivering different wavebands (Olson et al., 1966Olson R.L. Sayre R.M. Everett M.A. Effect of anatomic location and time on ultraviolet erythema.Arch Dermatol. 1966; 93: 211-215Crossref PubMed Scopus (57) Google Scholar) were used. The trunk appears to be the site most sensitive to erythema (Johnson et al., 1968Johnson B.E. Daniels Jr, F. Magnus I.A. Response of human skin to ultraviolet light.in: Giese A.C. Photophysiology Current Topics. Vol. IV. Academic Press, New York1968Crossref Google Scholar). This is true whether the erythemal response is assessed as degree of erythema 7 h following a measured ultraviolet dose (Schall and Alius, 1926Schall L. Alius H.-J. Zur Biologie des Ultraviolettlichts. Die Reaktion der menslichen Haut auf die Ultraviolettlichtbestrahlung (Erythemablauf).Strahlentherapie. 1926; 23: 161-180Google Scholar), as the dose producing minimal erythema detectable by the human eye (minimal erythemal dose (MED)) 8 h after administering a series of doses (Olson et al., 1966Olson R.L. Sayre R.M. Everett M.A. Effect of anatomic location and time on ultraviolet erythema.Arch Dermatol. 1966; 93: 211-215Crossref PubMed Scopus (57) Google Scholar), or assessed in both these ways 24 h after irradiation with a broad-band fluorescent ultraviolet B lamp (Waterston et al., 2004Waterston K. Naysmith L. Rees J.L. Physiological variation in the erythemal response to ultraviolet radiation and photoadaptation.J Invest Dermatol. 2004; 123: 958-964Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar). This recent study has usefully added to the existing evidence in favor of sites on the trunk for pre-treatment MED assessment. The back (usually mid- or upper) is commonly used for MED assessment because it is one of the more sensitive sites, if not the most sensitive site, in the majority of individuals. Although the abdomen may be more sensitive (Schall and Alius, 1926Schall L. Alius H.-J. Zur Biologie des Ultraviolettlichts. Die Reaktion der menslichen Haut auf die Ultraviolettlichtbestrahlung (Erythemablauf).Strahlentherapie. 1926; 23: 161-180Google Scholar; Olson et al., 1966Olson R.L. Sayre R.M. Everett M.A. Effect of anatomic location and time on ultraviolet erythema.Arch Dermatol. 1966; 93: 211-215Crossref PubMed Scopus (57) Google Scholar) 1Leslie KS, Lodge E, Garioch JJ: A comparison of narrowband (TL-01) ultraviolet B-induced erythemal response at different body sites. Br J Dermatol 151 (Suppl. 68): 103–104, 2004 (abstr).1Leslie KS, Lodge E, Garioch JJ: A comparison of narrowband (TL-01) ultraviolet B-induced erythemal response at different body sites. Br J Dermatol 151 (Suppl. 68): 103–104, 2004 (abstr). it is not always such a practically convenient test site. In their discussion, the authors questioned the value of MED testing before ultraviolet phototherapy. This was possibly meant just as a rhetorical device. Nevertheless, it is worth further clarifying the reasons as to why pre-treatment MED testing is clinically valuable despite the body-site variability in erythemal susceptibility. The primary purpose of pre-treatment MED testing is to determine a starting dose that will not cause uncomfortable (or more serious) erythema.Waterston et al., 2004Waterston K. Naysmith L. Rees J.L. Physiological variation in the erythemal response to ultraviolet radiation and photoadaptation.J Invest Dermatol. 2004; 123: 958-964Abstract Full Text Full Text PDF PubMed Scopus (39) Google Scholar found (as shown in their Fig 3) that if a whole-body starting dose of 50% MED (upper back, 24 h reading) was selected for their 15 study volunteers not one would have received a dose greater than the MED on any tested body site. If a 70% upper-back MED starting dose was used only four subjects would have received a dose slightly above the MED on the chest or lower back. The main conclusion for the clinical use of pre-treatment MED testing must be that the optimal test site is the upper back. Assuming, however, that the 15 volunteers were representative of the populations we treat, the chest or lower back would also be reasonable sites. Sites where the MED tends to be high (such as upper thigh) or very variable in relation to each individual's lowest MED (such as inner forearm) are not suitable if the MED is to be used to determine a safe whole-body treatment starting dose.