Electrical conductance: a controversial parameter in the evaluation of emollients in atopic dermatitis

Essential fatty acids are important in maintaining skin function and their deficiency is associated with scali-ness and increased transepidermal water loss (TEWL). This can be one of the pathogenic processes implicated in atopic dermatitis (AD). Several studies have assessed the value of essential fatty acid-enriched diets in AD but the benefits of topical γ-lino-lenic acid (GLA) therapy have been less well evaluated. The aims of this study were: a) to compare the effects of GLA-con-taining emollients and classical emollients, regarding clinical benefits, cutaneous hydration (by a conductance method) and TEWL; b) to assess the clinical relevance of these two biomet-rical methods (conductance and TEWL).

Twenty-three AD children were randomised into four groups, to compare three emollients containing GLA in different concentrations and one classical emollient. They were evaluated in eight visits for 12 weeks, using a clinical score and measurements of TEWL with the Tewameter™ and of cutaneous hydration with the Nova™.

Kruskal-Wallis statistical analysis showed significant differences in cutaneous hydration (P<0.05) between each of the three treatment groups and the control group. TEWL and clinical scores did not show statistically significant differences. During the study no children from the GLA groups developed eczematous lesions versus two children from the non-GLA group.

Discrepancies between conductance and TEWL measurements may represent false positive results of the former method due to electrical phenomena related to polarity of the GLA molecule or of other elements in the formulations. However, some differences in clinical evolution between the GLA and non-GLA groups require further studies to assess the possible additional benefits of topical emollients containing GLA.