Ultra-high frequency ultrasound detection of the dermo-epidermal junction: Its potential role in dermatology

Traditional high-frequency ultrasound (HFUS; 20 MHz) is a non-invasive method used to study skin in vivo but is not able to measure skin thickness accurately and to identify the dermal-epidermal junction (DEJ). Ultra-high frequency ultrasound (UHFUS; 70-100 MHz) has sub-millimetre resolution comparable to histology. The aim of this study was to identify, by UHFUS, the DEJ and to describe skin differences in healthy individuals by providing a measure of skin thickness, based on age and gender. We also described the bullous pemphigoid lesion. We enrolled 42 patients divided into 2 groups: A and B. Group A included 32 healthy volunteers aged 22-74 years. Group B consisted of 10 patients with bullous pemphigoid. For each patient in group A, 8 ultrasound (US) clips by 70 MHz probe were performed at forehead, cheek, nose, forearm, abdomen, chest, back and leg. For each patient in group B, 5 US images were acquired at blisters roofs and edges. In each US image, we measured thickness of stratum corneum (alpha-beta), epidermis (alpha-gamma) and epidermis plus dermis (alpha-delta). In both groups, we found the presence of 4 lines delimiting: the stratum corneum (the layer between alpha-line and beta-line), the epidermis (distance between alpha- and gamma-line), and the boundary between dermis and subcutis (delta-line). The gamma-line corresponds to the point of detachment of the bullae. The abdominal alpha-beta layer was thicker in males (p = 0.019) and alpha-delta thickness at cheeks (p < 0.001), chest (p = 0.007), back (p = 0.025) and forearm (p < 0.001). In females, alpha-gamma thickness of the back was greater (p = 0.005). In old people compared to young, we noticed an increase of alpha-beta layer at forehead and chest (p = 0.014), an increase of alpha-gamma layer at forearm (p = 0.001), back (p = 0.024) and leg (p = 0.010) and an increase of alpha-delta layer at forehead (p = 0.001) and nose (p = 0.049). UHFUS is an advanced imaging technique that can detect both the DEJ and the boundary between dermis and subcutaneous tissue so that epidermal and dermal thickness can be measured with good accuracy. Regarding gender and age, skin differences obtained with UHFUS were comparable to other non-invasive methods.