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Summary In this study, we characterized the stratum corneum barrier function in 39 patients with various keratinization disorders (autosomal dominant ichthyosis vulgaris [ADI] [n=7]. X-linked recessive ichthyosis [XRI] [n=6], autosomal recessive congenital ichthyosis [C1] [N=10]. dyskeratosis follicularis [Darier's disease: DD] [n=8], erythrokeratoderma variabilis [EKV] [n=8]). and 21 healthy volunteers, using two non-invasive methods: transepidermal water loss (TEWL) measuring outward transport of water through the skin by evaporimetry. and the vascular response to hexyl nicotinate (HN) penetration into the skin as determined by laser-Doppler flowmetry. Significantly increased TEWL values were found on the volar forearm in all three forms of ichthyosis, compared with the healthy control group, with the highest TEWL values in the CI group. The penetration of HN on the volar forearm was accelerated in patients with ADI. XRI and CI, as indicated by a shorter lag time (to) between HN application and initial vascular response. However, differentiation between CI and the other ichthyoses was not possible by this method. When using both methods in DD and EKV. no differences compared with the healthy controls could be detected on the volar forearm, where the skin was principally unaffected: only the measurements from the affected skin on alternative sites demonstrated significantly increased TEWL values. In ADI and CI. however, normal-appearing skin also showed impaired values. We conclude that both TEWL and the vascular response to penetration of HN are suitable methods to monitor the skin barrier function in keratinization disorders, and are helpful in discriminating between these disorders.

This study assesses the variability of two non-invasive methods of measuring stratum corneum barrier function in vivo. Transepidermal water loss (TEWL), and the vascular response to hexyl nicotinate (HN) penetration as determined by laser-Doppler flowmetry, were measured in a group of 21 healthy volunteers. Each time profile of the vascular response to HN penetration was analysed using the following parameters: the baseline cutaneous blood flow, the lag-time between application and initial response (t0), the time between application and maximum response (tmax), the maximum response, and the slope of the curve. TEWL measured on the left volar forearm showed a normal range of 3.9-7.6 g/m2h and a small inter-individual variability [coefficient of variation (CV) 19.4%]. TEWL values at three other forearm sites did not show differences of clinical importance compared with the left volar forearm. The parameters of the vascular response to HN penetration spanned a wider normal range than the TEWL values (CV between 33 and 52%). Repeat measurements after a 1-2 month interval showed highly reproducible individual TEWL values. The mean difference between first and second measurements was only 0.03 g/m2h; the relative difference 0.6%. The intra-individual reproducibility of t0 and tmax. for HN penetration was also high (relative differences of 2.8 and 3.1%, respectively). The other vascular response parameters were less reproducible (relative differences of 6.9-18.6%). We conclude that TEWL and selected parameters of HN penetration, as non-invasive tests of the stratum corneum barrier function, yield reproducible results and are hence useful for investigations assessing the skin barrier function in various disorders.