Ultrasound structure and digital image analysis of the subepidermal low echogenic band in aged human skin: diurnal changes and interindividual variability.

Subepidermal low-echogenic band is a consistent echostructural finding in aged and photodamaged skin. The thickness of subepidermal low-echogenic band is considered to closely reflect the degree of cutaneous aging and its use for the monitoring of the severity of photoaging and the efficacy of drugs is rapidly expanding. We investigated subepidermal low-echogenic band structure in 23 old healthy volunteers (ages 75-100) with a high-frequency ultrasound scanner (B-mode, 20 MHz). Images were collected from the volar fore-arm twice daily: in the morning before getting up and 12 h later. To assess the severity of subepidermal low-echogenic band, echogenicity of the subepidermal region was determined by the image analysis and compared with visual scoring and subepidermal low-echogenic band thickness. All three methods gave consistent results, image analysis being the most sensitive, reliable, and bias-free. Significant interindividual variability of subepidermal low-echogenic band echostructure was revealed. Moreover, circadian variability of subepidermal low-echogenic band echogenicity was observed. These major interindividual and diurnal variations of subepidermal low-echogenic band suggest that this band does not only represent an irreversible structural change but also a redistribution of fluid in the aged dermis. Diurnal variations in the subepidermal low-echogenic band would limit the use of this parameter in studies of skin aging, photoaging, and efficiency of medication.